{"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$$\u0027]]\n }\n });\n\u003c/script\u003e\n\u003cscript type\u003d\"text/javascript\" async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS_HTML-full\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"\u003cp\u003eGohary is playing a variant of Hotwheels and wants to finish a certain level.\u003c/p\u003e\u003cp\u003e That level consists of a platform with some cars in it. \u003c/p\u003e \u003cp\u003eThe cars have the following behavior:\u003c/p\u003e\u003cul\u003e \u003cli\u003e Initially, they point in one direction, (left: 0, right: 1). \u003c/li\u003e\u003cli\u003e They move in the direction they are currently facing, as long as there are no obstacles. \u003c/li\u003e\u003cli\u003e If two cars collide, they will flip their direction immediately. \u003c/li\u003e\u003cli\u003e When a car reaches one end of the platform, it falls. \u003c/li\u003e\u003c/ul\u003e\u003cp\u003eThe platform is $$$L$$$ blocks long, extending from the coordinate $$$0$$$, to $$$L$$$. Above it, there will be $$$C$$$ cars. The $$$i-th$$$ car will be located at $$$p_i$$$ facing to the direction $$$d_i$$$. All cars will advance with a speed of $$$1$$$ block per second.\u003c/p\u003e\u003cp\u003e Gohary wants to figure out many seconds it will take for the platform to be empty.\u003c/p\u003e\u003cp\u003eFor this problem purposes, consider the size of a car to be a single point. No two cars will share the same initial $$$x$$$ coordinate.\u003c/p\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\u003cp\u003eThe first line of the input contains two integers $$$L$$$ $$$\\left(2\\leq L \\leq 10^{16}\\right)$$$ and $$$C$$$ $$$\\left(1 \\leq C \\leq 10^4 \\right)$$$.\u003c/p\u003e\u003cp\u003eEach of the following $$$C$$$ lines contains two integers $$$p_i$$$ $$$\\left(0 \u0026lt; p_i \u0026lt; L\\right)$$$ and $$$d_i$$$ $$$\\left(d_i \\in \\{0, 1\\}\\right)$$$.\u003c/p\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\u003cp\u003eThe time in seconds that must pass for the platform to be empty.\u003c/p\u003e"}},{"title":"Sample 1","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\u003e3 2\n1 1\n2 0\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e2\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"Sample 2","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 2\n1 0\n2 1\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e3\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}}]}