{"trustable":false,"prependHtml":"\u003cstyle type\u003d\u0027text/css\u0027\u003e\n .input, .output {\n border: 1px solid #888888;\n }\n .output {\n margin-bottom: 1em;\n position: relative;\n top: -1px;\n }\n .output pre, .input pre {\n background-color: #EFEFEF;\n line-height: 1.25em;\n margin: 0;\n padding: 0.25em;\n }\n \u003c/style\u003e\n \u003clink rel\u003d\"stylesheet\" href\u003d\"//codeforces.org/s/96598/css/problem-statement.css\" type\u003d\"text/css\" /\u003e\u003cscript\u003e window.katexOptions \u003d { disable: true }; \u003c/script\u003e\n\u003cscript type\u003d\"text/x-mathjax-config\"\u003e\n MathJax.Hub.Config({\n tex2jax: {\n inlineMath: [[\u0027$$$\u0027,\u0027$$$\u0027], [\u0027$\u0027,\u0027$\u0027]],\n displayMath: [[\u0027$$$$$$\u0027,\u0027$$$$$$\u0027], [\u0027$$\u0027,\u0027$$\u0027]]\n }\n });\n\u003c/script\u003e\n\u003cscript type\u003d\"text/javascript\" async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS_HTML-full\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"\u003cp\u003e The key principle of the \"\u003cspan\u003e\u003cspan\u003e\u003cspan\u003eAbijith\u0027s\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e Matching\" dating agency is \"Everybody knows that opposites attract\". The \"\u003cspan\u003e\u003cspan\u003e\u003cspan\u003eAbijith\u0027s\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e Matching\" matchmakers have classified each registered customer by his interests and assigned to the \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003ei\u003c/i\u003e\u003c/span\u003e\u003cspan\u003e-th\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e client number \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e\u003ci\u003ei\u003c/i\u003e\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e (\u003cspan\u003e - 10 ≤ \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e\u003ci\u003ei\u003c/i\u003e\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e ≤ 10\u003c/span\u003e). Of course, one number can be assigned to any number of customers.\u003c/p\u003e \n\u003cp\u003e \"\u003cspan\u003e\u003cspan\u003e\u003cspan\u003eAbijith\u0027s\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e Matching\" wants to advertise its services and publish the number of opposite couples, that is, the couples who have opposite values of \u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003c/span\u003e. Each couple consists of exactly two clients. The customer can be included in a couple an arbitrary number of times. Help him and write the program that will find the sought number by the given sequence \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e1\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e, \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e, ..., \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e\u003ci\u003en\u003c/i\u003e\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e. For example, if \u003cspan\u003e\u003ci\u003et\u003c/i\u003e \u003d (1, - 1, 1, - 1)\u003c/span\u003e, then any two elements \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e\u003ci\u003ei\u003c/i\u003e\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e and \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e\u003ci\u003ej\u003c/i\u003e\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e form a couple if \u003cspan\u003e\u003ci\u003ei\u003c/i\u003e\u003c/span\u003e and \u003cspan\u003e\u003ci\u003ej\u003c/i\u003e\u003c/span\u003e have different parity. Consequently, in this case the sought number equals 4.\u003c/p\u003e \n\u003cp\u003e Of course, a client can\u0027t form a couple with him/herself.\u003c/p\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\u003cp\u003e The first line of the input data contains an integer \u003cspan\u003e\u003ci\u003en\u003c/i\u003e\u003c/span\u003e (\u003cspan\u003e1 ≤ \u003ci\u003en\u003c/i\u003e ≤ 10\u003csup\u003e5\u003c/sup\u003e\u003c/span\u003e) which represents the number of registered clients of the \"\u003cspan\u003e\u003cspan\u003e\u003cspan\u003eAbijith\u0027s\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e Matching\". The second line contains a sequence of integers \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e1\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e, \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e, ..., \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e\u003ci\u003en\u003c/i\u003e\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e (\u003cspan\u003e - 10 ≤ \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e\u003ci\u003ei\u003c/i\u003e\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e ≤ 10\u003c/span\u003e), \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003csub\u003e\u003ci\u003ei\u003c/i\u003e\u003c/sub\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e — is the parameter of the \u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003cspan\u003e\u003ci\u003ei\u003c/i\u003e\u003c/span\u003e-th\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e customer that has been assigned to the customer by the result of the analysis of his interests.\u003c/p\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\u003cp\u003e Print the number of couples of customs with opposite \u003cspan\u003e\u003ci\u003et\u003c/i\u003e\u003c/span\u003e. The opposite number for \u003cspan\u003e\u003ci\u003ex\u003c/i\u003e\u003c/span\u003e is number \u003cspan\u003e - \u003ci\u003ex\u003c/i\u003e\u003c/span\u003e (\u003cspan\u003e0\u003c/span\u003e is opposite to itself). Couples that only differ in the clients\u0027 order are considered the same.\u003c/p\u003e \n\u003cp\u003e \u003cstrong\u003eNote\u003c/strong\u003e that the answer to the problem can be large enough, so you must use the 64-bit integer type for calculations.\u003c/p\u003e \n\u003cp\u003e \u003cstrong\u003eC++ users\u003c/strong\u003e: Please, do not use the %\u003cspan\u003e\u003cspan\u003e\u003cspan\u003elld\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e \u003cspan\u003e\u003cspan\u003e\u003cspan\u003especificator\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e to read or write 64-bit integers in \u003cstrong\u003eС++\u003c/strong\u003e. It is preferred to use \u003cspan\u003e\u003cspan\u003e\u003cspan\u003ecin\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e, \u003cspan\u003e\u003cspan\u003e\u003cspan\u003ecout\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e streams or the %\u003cspan\u003e\u003cspan\u003e\u003cspan\u003eI64d\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e \u003cspan\u003e\u003cspan\u003e\u003cspan\u003especificator\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/p\u003e"}},{"title":"Sample Input","value":{"format":"HTML","content":"\u003cdiv\u003e \n \u003cdiv\u003e\n Input\n \u003c/div\u003e \n \u003cdiv\u003e\n 5\n \u003c/div\u003e \n \u003cdiv\u003e\n -3 3 0 0 3\n \u003c/div\u003e \n\u003c/div\u003e \n\u003cdiv\u003e\n \u0026nbsp;\n\u003c/div\u003e \n\u003cdiv\u003e \n \u003cdiv\u003e\n Input\n \u003c/div\u003e \n \u003cdiv\u003e\n 3\n \u003c/div\u003e \n \u003cdiv\u003e\n 0 0 0\n \u003c/div\u003e \n\u003c/div\u003e"}},{"title":"Sample Output","value":{"format":"HTML","content":"\u003cdiv\u003e \n \u003cdiv\u003e\n Output\n \u003c/div\u003e \n \u003cdiv\u003e\n 3\n \u003c/div\u003e \n \u003cdiv\u003e \n \u003cdiv\u003e \n \u003cdiv\u003e\n \u0026nbsp;\n \u003c/div\u003e \n \u003cdiv\u003e\n Output\n \u003c/div\u003e \n \u003cdiv\u003e\n 3\n \u003c/div\u003e \n \u003c/div\u003e \n \u003cp\u003e \u0026nbsp;\u003c/p\u003e \n \u003c/div\u003e \n\u003c/div\u003e"}},{"title":"Hint","value":{"format":"HTML","content":"\u003cp\u003e In the first sample the couples of opposite clients are: \u003cspan\u003e(1,2), (1,5) \u0026amp; (3,4)\u003c/span\u003e.\u003c/p\u003e \n\u003cp\u003e In the second sample any couple of clients is opposite.\u003c/p\u003e"}}]}