{"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":"MD","content":"给定n对整数(a1,b1),(a2,b2),…,(an,bn), 所有的整数不同 , 范围从1到2⋅n。\n我们称一个整数序列为x1 x2…x2k是一个“好序列”:\n如果 : x1 \u003c x2 \u003e x3 \u003c…\u003c x2k−2 \u003e x2k−1 \u003c x2k \n或 者 : x1 \u003e x2 \u003c x3 \u003e…\u003e x2k−2 \u003c x2k−1 \u003e x2k。\n\nlwj想考考你:\n找出一个最大的整数对子集,满足这些整数对按一定顺序组成的序列\nai1,bi1,ai2,bi2,…,ait,bit,这个序列是一个“好序列”;\n"}},{"title":"Input","value":{"format":"MD","content":"输入\n第一行包含一个整数n (2≤n≤300000)——整数对的数量。\n每个下n行包含两个数字,ai和bi (1≤ai, bi≤2⋅n) 整数对的元素。\n保证所有整数对是不同的,也就是说,整数1到2⋅n每个出现一次。\n"}},{"title":"Output","value":{"format":"MD","content":"输出\n在第一行中打印一个整数t—答案中的对的数量。\n然后打印t个不同的整数i1,i2,…\n"}},{"title":"Examples","value":{"format":"MD","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\u003e5\n1 7\n6 4\n2 10\n9 8\n3 5\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\u003e3\n1 5 3\n\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\u003e3\n5 4\n3 2\n6 1\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\u003e3\n3 2 1\n\u003c/pre\u003e\n \u003c/div\u003e\n\u003c/div\u003e"}},{"title":"Note","value":{"format":"MD","content":"The final sequence in the first example is 1\u003c7\u003e3\u003c5\u003e2\u003c10\nThe final sequence in the second example is 6\u003e1\u003c3\u003e2\u003c5\u003e4\n"}}]}