{"trustable":true,"prependHtml":"\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 async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS-MML_HTMLorMML\" type\u003d\"text/javascript\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"\u003cdiv class\u003d\"panel_content\"\u003en pairs of couples are invited to a party. Due to venue constraints, only 1 person from each couple can attend. Among the 2n people, there are significant conflicts between some individuals (except for couples, who have no conflicts). Two individuals with conflicts will not appear at the party at the same time. Is it possible for n people to attend the party at the same time?\u003c/div\u003e"}},{"title":"Input","value":{"format":"HTML","content":"n: represents the number of couples invited (n \u0026lt;\u003d 1000)\u003cbr\u003em: represents the number of conflicting relationships (m \u0026lt; (n - 1) * (n - 1))\u003cbr\u003e\u003cbr\u003e In the next m lines, each line will contain 4 numbers: A1, A2, C1, C2 \u003cbr\u003e A1, A2 represent the couple\u0027s numbers \u003cbr\u003e C1, C2 represent whether it is the wife or the husband, 0 represents the wife, 1 represents the husband \u003cbr\u003e Couple numbers range from 0 to n - 1 \u003cbr\u003e"}},{"title":"Output","value":{"format":"HTML","content":"If a situation exists, output YES \u003cbr\u003eOtherwise, output NO \u003cbr\u003e"}},{"title":"Sample","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\u003e2 \r\n1\r\n0 1 1 1 \r\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003eYES\r\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e"}}]}