{"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\n\u003cscript\u003e\n window.katexOptions \u003d {\n delimiters: [\n {left: \u0027$$$$$$\u0027, right: \u0027$$$$$$\u0027, display: true},\n {left: \u0027$$$\u0027, right: \u0027$$$\u0027, display: false},\n {left: \u0027$$\u0027, right: \u0027$$\u0027, display: true},\n {left: \u0027$\u0027, right: \u0027$\u0027, display: false}\n ]\n };\n\u003c/script\u003e\n","sections":[{"title":"","value":{"format":"HTML","content":"\u003cstyle type\u003d\u0027text/css\u0027\u003e .input, .output {border: 1px solid #888888;} .output {margin-bottom:1em;position:relative;top:-1px;} .output pre,.input pre {background-color:#EFEFEF;line-height:1.25em;margin:0;padding:0.25em;} .title {background-color:#FFFFFF;border-bottom: 1px solid #888888;font-family:arial;font-weight:bold;padding:0.25em;} \u003c/style\u003e \u003cscript type\u003d\"text/x-mathjax-config\"\u003e\n MathJax.Hub.Config({\n tex2jax: {inlineMath: [[\u0027$$$\u0027,\u0027$$$\u0027]], displayMath: [[\u0027$$$$$$\u0027,\u0027$$$$$$\u0027]]}\n });\n \u003c/script\u003e\n \u003cscript type\u003d\"text/javascript\" async\n src\u003d\"https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config\u003dTeX-AMS-MML_HTMLorMML\"\u003e\n \u003c/script\u003e\n\u003cp\u003e给你n个点,请你构造一个图,这个图必须符合以下几个性质: \u003c/p\u003e \n\u003cul\u003e \n \u003cli\u003e 它是一个简单无向图,没有重边和自环。 \u003c/li\u003e \n \u003cli\u003e 图的总边数为素数。 \u003c/li\u003e \n \u003cli\u003e 每个顶点的度为素数。 \u003c/li\u003e\n\u003c/ul\u003e \n\u003cp\u003e比如现在 n \u003d 4。第一个图不合法因为顶点 2 (或 4) 的度为1,不是素数。第二图也不合法,因为总边数之和为4,不是素数。第三个图是合法的。 \u003c/p\u003e \n\u003ccenter\u003e \n \u003cimg class\u003d\"tex-graphics\" SRC\u003d\"CDN_BASE_URL/67260c86f74df1b62bb91b51d977e60e?v\u003d1587111693\" style\u003d\"max-width: 100.0%;max-height: 100.0%;\"\u003e\n\u003c/center\u003e \n\u003cp\u003e图可以不连通。\u003c/p\u003e "}},{"title":"Input","value":{"format":"HTML","content":"\u003cp\u003e输入仅包含一个正整数 n (3 \u003c\u003dn \u003c\u003d 1000)。\u003c/p\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\u003cp\u003e如果没有符合题意的图,输出-1。\u003c/p\u003e \n\u003cp\u003e否则,第一行输出一个整数数 m,表示构造的图的边数。接下来m行,每行两个正整数,表示每条边的两个端点。 \n\u003cp\u003e如果有多种不同的解法,输出任意一种即可。\u003c/p\u003e "}},{"title":"Examples","value":{"format":"HTML","content":"\u003cdiv class\u003d\"sample-test\"\u003e \n \u003cdiv class\u003d\"input\"\u003e \n \u003cdiv class\u003d\"title\"\u003e\n Input\n \u003c/div\u003e \n \u003cpre\u003e4\n\u003c/pre\u003e\n \u003c/div\u003e \n \u003cdiv class\u003d\"output\"\u003e \n \u003cdiv class\u003d\"title\"\u003e\n Output\n \u003c/div\u003e \n \u003cpre\u003e5\n1 2\n1 3\n2 3\n2 4\n3 4\u003c/pre\u003e\n \u003c/div\u003e \n \u003cdiv class\u003d\"input\"\u003e \n \u003cdiv class\u003d\"title\"\u003e\n Input\n \u003c/div\u003e \n \u003cpre\u003e8\n\u003c/pre\u003e\n \u003c/div\u003e \n \u003cdiv class\u003d\"output\"\u003e \n \u003cdiv class\u003d\"title\"\u003e\n Output\n \u003c/div\u003e \n \u003cpre\u003e13\n1 2\n1 3\n2 3\n1 4\n2 4\n1 5\n2 5\n1 6\n2 6\n1 7\n1 8\n5 8\n7 8\n\u003c/pre\u003e\n \u003c/div\u003e\n\u003c/div\u003e"}},{"title":"Note","value":{"format":"HTML","content":"\n\u003cp\u003e第二个样例可以这样构造:\n\u003ccenter\u003e \n \u003cimg class\u003d\"tex-graphics\" SRC\u003d\"CDN_BASE_URL/f8dd46bcaf61705c6f9b9dcf55b28c66?v\u003d1587111693\" style\u003d\"max-width: 100.0%;max-height: 100.0%;\"\u003e\n\u003c/center\u003e"}}]}