A. LLPStime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputThis 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[p1p2... pk] = sp1sp2... spk (1  ≤  p1 < p2 < ... < pk  ≤  |s|) a subsequence of string s = s1s2... s|s|, where |s| is the length of string s. For example, strings "abcb", "b" and "abacaba" are subsequences of string "abacaba".String x = x1x2... x|x| is lexicographically larger than string y = y1y2... y|y| if either |x| > |y| and x1 = y1, x2 = y2, ..., x|y| = y|y|, or there exists such number r (r < |x|, r < |y|) that x1 = y1, x2 = y2, ..., xr = yr and xr  +  1 > yr  +  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 = s1s2... s|s| is a palindrome if it matches string rev(s) = s|s|s|s| - 1... s1. 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".InputThe only input line contains a non-empty string s consisting of lowercase English letters only. Its length does not exceed 10.OutputPrint the lexicographically largest palindromic subsequence of string s.ExamplesInputradarOutputrrInputbowwowwowOutputwwwwwInputcodeforcesOutputsInputmississippOutputssssNoteAmong 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".
Inputradar
Outputrr
['binary search', 'bitmasks', 'brute force', 'greedy', 'implementation', 'strings', '*800']