{"trustable":true,"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$$\u0027]]\n }\n });\n\u003c/script\u003e\n\u003cscript type\u003d\"text/javascript\" async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS_HTML-full\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"\u003cp\u003eBob has a string $$$s$$$ consisting of lowercase English letters. He defines $$$s\u0027$$$ to be the string after removing all \"\u003cspan class\u003d\"tex-font-style-tt\"\u003ea\u003c/span\u003e\" characters from $$$s$$$ (keeping all other characters in the same order). He then generates a new string $$$t$$$ by concatenating $$$s$$$ and $$$s\u0027$$$. In other words, $$$t\u003ds+s\u0027$$$ (look at notes for an example).\u003c/p\u003e\u003cp\u003eYou are given a string $$$t$$$. Your task is to find some $$$s$$$ that Bob could have used to generate $$$t$$$. It can be shown that if an answer exists, it will be unique.\u003c/p\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\u003cp\u003eThe first line of input contains a string $$$t$$$ ($$$1 \\leq |t| \\leq 10^5$$$) consisting of lowercase English letters.\u003c/p\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\u003cp\u003ePrint a string $$$s$$$ that could have generated $$$t$$$. It can be shown if an answer exists, it is unique. If no string exists, print \"\u003cspan class\u003d\"tex-font-style-tt\"\u003e:(\u003c/span\u003e\" (without double quotes, there is no space between the characters).\u003c/p\u003e"}},{"title":"Examples","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\u003eaaaaa\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003eaaaaa\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"","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\u003eaacaababc\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e:(\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"","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\u003eababacacbbcc\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003eababacac\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"","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\u003ebaba\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e:(\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}},{"title":"Note","value":{"format":"HTML","content":"\u003cp\u003eIn the first example, we have $$$s \u003d $$$ \"\u003cspan class\u003d\"tex-font-style-tt\"\u003eaaaaa\u003c/span\u003e\", and $$$s\u0027 \u003d $$$ \"\u003cspan class\u003d\"tex-font-style-tt\"\u003e\u003c/span\u003e\".\u003c/p\u003e\u003cp\u003eIn the second example, no such $$$s$$$ can work that will generate the given $$$t$$$.\u003c/p\u003e\u003cp\u003eIn the third example, we have $$$s \u003d $$$ \"\u003cspan class\u003d\"tex-font-style-tt\"\u003eababacac\u003c/span\u003e\", and $$$s\u0027 \u003d $$$ \"\u003cspan class\u003d\"tex-font-style-tt\"\u003ebbcc\u003c/span\u003e\", and $$$t \u003d s + s\u0027 \u003d $$$ \"\u003cspan class\u003d\"tex-font-style-tt\"\u003eababacacbbcc\u003c/span\u003e\".\u003c/p\u003e"}}]}