B. Two-gramtime limit per test1 secondmemory limit per test256 megabytesinputstandard inputoutputstandard outputTwo-gram is an ordered pair (i.e. string of length two) of capital Latin letters. For example, "AZ", "AA", "ZA" — three distinct two-grams.You are given a string s consisting of n capital Latin letters. Your task is to find any two-gram contained in the given string as a substring (i.e. two consecutive characters of the string) maximal number of times. For example, for string s = "BBAABBBA" the answer is two-gram "BB", which contained in s three times. In other words, find any most frequent two-gram.Note that occurrences of the two-gram can overlap with each other.InputThe first line of the input contains integer number n (2 \le n \le 100) — the length of string s. The second line of the input contains the string s consisting of n capital Latin letters.OutputPrint the only line containing exactly two capital Latin letters — any two-gram contained in the given string s as a substring (i.e. two consecutive characters of the string) maximal number of times.ExamplesInput7ABACABAOutputABInput5ZZZAAOutputZZNoteIn the first example "BA" is also valid answer.In the second example the only two-gram "ZZ" can be printed because it contained in the string "ZZZAA" two times.
Input7ABACABA
OutputAB
['implementation', 'strings', '*900']