{"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$$\u0027]]\n }\n });\n\u003c/script\u003e\n\u003cscript type\u003d\"text/javascript\" async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS_HTML-full\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"\u003cstyle type\u003d\u0027text/css\u0027\u003e .input, .output {border: 1px solid #888888;} .output {margin-bottom:1em;position:relative;top:-1px;} .output pre,.input pre {background-color:#EFEFEF;line-height:1.25em;margin:0;padding:0.25em;} .title {background-color:#FFFFFF;border-bottom: 1px solid #888888;font-family:arial;font-weight:bold;padding:0.25em;} \u003c/style\u003e \u003cscript type\u003d\"text/x-mathjax-config\"\u003e\n MathJax.Hub.Config({\n tex2jax: {inlineMath: [[\u0027$$$\u0027,\u0027$$$\u0027]], displayMath: [[\u0027$$$$$$\u0027,\u0027$$$$$$\u0027]]}\n });\n \u003c/script\u003e\n \u003cscript type\u003d\"text/javascript\" async\n src\u003d\"https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js?config\u003dTeX-AMS-MML_HTMLorMML\"\u003e\n \u003c/script\u003e\n\u003cp\u003e帅气的Pof学长有一个由小写英文字母构成的字符串 s . 他将 s\u0027 定义为删去所有 \"\u003cspan class\u003d\"tex-font-style-tt\"\u003ea\u003c/span\u003e\" 的 s (除去\u0027a\u0027外的其他所有字母都按照原字符串中的顺序保留). 接着,他将这两个字符串拼在一起组成一个新的字符串,即令t\u003ds+s\u0027\u003c/p\u003e\n\u003cp\u003e如今给出 t. 你的任务是找到一个满足条件的 s 使得Pof学长可以用这个字符串按照定义生成 t. 可以被证明,如果答案存在,那么答案唯一.\u003c/p\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\u003cp\u003e第一行包含一个字符串 t (1 \u003c\u003d |t| \u003c\u003d 10^5) ,保证其只由小写英文字母构成.\u003c/p\u003e\n"}},{"title":"Output","value":{"format":"HTML","content":"\u003cp\u003e输出一个字符串 s. 如果这样的s不存在,那么输出一行\"\u003cspan class\u003d\"tex-font-style-tt\"\u003e:(\u003c/span\u003e\" (不包含引号).\u003c/p\u003e"}},{"title":"Examples","value":{"format":"HTML","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\u003eaaaaa\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\u003eaaaaa\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\u003eaacaababc\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\u003e:(\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\u003eababacacbbcc\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\u003eababacac\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\u003ebaba\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\u003e:(\n\u003c/pre\u003e\n \u003c/div\u003e\n\u003c/div\u003e"}},{"title":"Note","value":{"format":"HTML","content":"\u003cp\u003e在第一个样例中, s \u003d \"\u003cspan class\u003d\"tex-font-style-tt\"\u003eaaaaa\u003c/span\u003e\", s\u0027 \u003d \"\u003cspan class\u003d\"tex-font-style-tt\"\u003e\u003c/span\u003e\".\u003c/p\u003e\n\u003cp\u003e在第二个样例中,没有一个 s 能够生成给出的 t.\u003c/p\u003e\n\u003cp\u003e在第三个样例中, s \u003d \"\u003cspan class\u003d\"tex-font-style-tt\"\u003eababacac\u003c/span\u003e\", s\u0027 \u003d \"\u003cspan class\u003d\"tex-font-style-tt\"\u003ebbcc\u003c/span\u003e\", t \u003d s + s\u0027 \u003d \"\u003cspan class\u003d\"tex-font-style-tt\"\u003eababacacbbcc\u003c/span\u003e\".\u003c/p\u003e"}}]}