{"raw_statement":[{"iden":"statement","content":"Mike has a string _s_ consisting of only lowercase English letters. He wants to **change exactly one** character from the string so that the resulting one is a palindrome.\n\nA palindrome is a string that reads the same backward as forward, for example strings \"_z_\", \"_aaa_\", \"_aba_\", \"_abccba_\" are palindromes, but strings \"_codeforces_\", \"_reality_\", \"_ab_\" are not."},{"iden":"input","content":"The first and single line contains string _s_ (1 ≤ |_s_| ≤ 15)."},{"iden":"output","content":"Print \"_YES_\" (without quotes) if Mike can change **exactly** one character so that the resulting string is palindrome or \"_NO_\" (without quotes) otherwise."},{"iden":"examples","content":"Input\n\nabccaa\n\nOutput\n\nYES\n\nInput\n\nabbcca\n\nOutput\n\nNO\n\nInput\n\nabcda\n\nOutput\n\nYES"}],"translated_statement":[{"iden":"statement","content":"Mike 有一个仅由小写英文字母组成的字符串 #cf_span[s]。他希望将字符串中的*恰好一个*字符进行修改，使得修改后的字符串成为回文串。\n\n回文串是指正读和反读都相同的字符串，例如字符串 \"_z_\"、\"_aaa_\"、\"_aba_\"、\"_abccba_\" 是回文串，但字符串 \"_codeforces_\"、\"_reality_\"、\"_ab_\" 不是。\n\n第一行且仅有一行包含字符串 #cf_span[s]（#cf_span[1 ≤ |s| ≤ 15]）。\n\n如果 Mike 能够通过修改*恰好一个*字符使结果字符串成为回文串，则输出 \"_YES_\"（不含引号）；否则输出 \"_NO_\"（不含引号）。"},{"iden":"input","content":"第一行且仅有一行包含字符串 #cf_span[s]（#cf_span[1 ≤ |s| ≤ 15]）。"},{"iden":"output","content":"如果 Mike 能够通过修改*恰好一个*字符使结果字符串成为回文串，则输出 \"_YES_\"（不含引号）；否则输出 \"_NO_\"（不含引号）。"},{"iden":"examples","content":"输入\nabccaa\n输出\nYES\n输入\nabbcca\n输出\nNO\n输入\nabcda\n输出\nYES"}],"sample_group":[],"show_order":[],"formal_statement":"**Definitions**  \nLet $ s \\in \\Sigma^* $ be a string of length $ n $, where $ \\Sigma = \\{a, b, \\dots, z\\} $ and $ 1 \\leq n \\leq 15 $.\n\n**Constraints**  \n1. $ |s| = n $, with $ 1 \\leq n \\leq 15 $  \n2. Each character of $ s $ is a lowercase English letter.\n\n**Objective**  \nDetermine whether there exists exactly one index $ i \\in \\{1, \\dots, n\\} $ and a character $ c \\in \\Sigma $ such that replacing $ s[i] $ with $ c $ yields a palindrome, and the resulting string is not identical to $ s $.  \n\nEquivalently, define $ s' $ such that $ s'[j] = s[j] $ for all $ j \\neq i $, and $ s'[i] = c \\neq s[i] $, and $ s' $ is a palindrome.  \nOutput \"YES\" if such $ i $ and $ c $ exist; otherwise, output \"NO\".","simple_statement":null,"has_page_source":false}