This problem's actual name, "Lexicographically Largest Palindromic Subsequence" is too long to fit into the page headline. You are given string s consisting of lowercase English letters only. Find its lexicographically largest palindromic subsequence. We'll call a non-empty string s p 1 p 2 ... p k = s p 1 s p 2 ... s p k ( 1 ≤ p 1 < p 2 < ... < p k ≤ | s | ) a subsequence of string s = s 1 s 2 ... s | s | , where | s | is the length of string s . For example, strings " abcb ", " b " and " abacaba " are subsequences of string " abacaba ". String x = x 1 x 2 ... x | x | is lexicographically larger than string y = y 1 y 2 ... y | y | if either | x | > | y | and x 1 = y 1 , x 2 = y 2 , ..., x | y | = y | y | , or there exists such number r ( r < | x | , r < | y | ) that x 1 = y 1 , x 2 = y 2 , ..., x r = y r and x r + 1 > y r + 1 . Characters in the strings are compared according to their ASCII codes. For example, string " ranger " is lexicographically larger than string " racecar " and string " poster " is lexicographically larger than string " post ". String s = s 1 s 2 ... s | s | is a palindrome if it matches string rev ( s ) = s | s | s | s | - 1 ... s 1 . In other words, a string is a palindrome if it reads the same way from left to right and from right to left. For example, palindromic strings are " racecar ", " refer " and " z ". The only input line contains a non-empty string s consisting of lowercase English letters only. Its length does not exceed 10 . Print the lexicographically largest palindromic subsequence of string s . Among all distinct subsequences of string " radar " the following ones are palindromes: " a ", " d ", " r ", " aa ", " rr ", " ada ", " rar ", " rdr ", " raar " and " radar ". The lexicographically largest of them is " rr ".