{"trustable":false,"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":"给定n个A,n个B,n个C。要组成一个长度为3*n的字符串。\u003c/br\u003e\n需要满足,任意一个前缀中A出现的次数不少于B的数量,B出现的数量不少于C的数量。\u003c/br\u003e\nn\u003d2时,有5个满足条件的字符串:AABBCC , AABCBC , ABABCC , ABACBC and ABCABC . \u003c/br\u003e\n输出满足条件的字符串数量。"}},{"title":"Input","value":{"format":"HTML","content":"多组输入数据\u003c/br\u003e\n每行一个整数n, (0 \u0026lt;\u003d n \u0026lt;\u003d 60 ). "}},{"title":"Output","value":{"format":"HTML","content":"每组测试数据,输出两行,第一行一个整数,表示结果。\n第二行,一个换行符。\n"}},{"title":"Sample Input","value":{"format":"HTML","content":"\u003cpre\u003e2\n\n3\u003c/pre\u003e"}},{"title":"Sample Output","value":{"format":"HTML","content":"\u003cpre\u003e5\n\n42\u003c/pre\u003e"}}]}