{"trustable":true,"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$$\u0027]]\n }\n });\n\u003c/script\u003e\n\u003cscript type\u003d\"text/javascript\" async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS_HTML-full\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"\u003cp\u003eYou are given a Young diagram. \u003c/p\u003e\u003cp\u003eGiven diagram is a histogram with $$$n$$$ columns of lengths $$$a_1, a_2, \\ldots, a_n$$$ ($$$a_1 \\geq a_2 \\geq \\ldots \\geq a_n \\geq 1$$$).\u003c/p\u003e\u003ccenter\u003e \u003cimg class\u003d\"tex-graphics\" src\u003d\"CDN_BASE_URL/a932f2f9a2518d684d0e217e4029f367?v\u003d1715603130\" style\u003d\"max-width: 100.0%;max-height: 100.0%;\"\u003e \u003cspan class\u003d\"tex-font-size-small\"\u003eYoung diagram for $$$a\u003d[3,2,2,2,1]$$$.\u003c/span\u003e \u003c/center\u003e\u003cp\u003eYour goal is to find the largest number of non-overlapping dominos that you can draw inside of this histogram, a domino is a $$$1 \\times 2$$$ or $$$2 \\times 1$$$ rectangle.\u003c/p\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\u003cp\u003eThe first line of input contain one integer $$$n$$$ ($$$1 \\leq n \\leq 300\\,000$$$): the number of columns in the given histogram.\u003c/p\u003e\u003cp\u003eThe next line of input contains $$$n$$$ integers $$$a_1, a_2, \\ldots, a_n$$$ ($$$1 \\leq a_i \\leq 300\\,000, a_i \\geq a_{i+1}$$$): the lengths of columns.\u003c/p\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\u003cp\u003eOutput one integer: the largest number of non-overlapping dominos that you can draw inside of the given Young diagram.\u003c/p\u003e"}},{"title":"Examples","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e5\n3 2 2 2 1\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e4\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"Note","value":{"format":"HTML","content":"\u003cp\u003eSome of the possible solutions for the example:\u003c/p\u003e\u003cp\u003e\u003cimg class\u003d\"tex-graphics\" src\u003d\"CDN_BASE_URL/645e25ed57189db51041d0494b8ef776?v\u003d1715603130\" style\u003d\"max-width: 100.0%;max-height: 100.0%;\"\u003e \u003cimg class\u003d\"tex-graphics\" src\u003d\"CDN_BASE_URL/7ea0dbe099054f634b682a323351cb92?v\u003d1715603130\" style\u003d\"max-width: 100.0%;max-height: 100.0%;\"\u003e\u003c/p\u003e"}}]}