CF977B.Two-gram

普及/提高-

通过率：0%

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题目描述

Two-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.

输入格式

The 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.

输出格式

Print 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.

输入输出样例

输入#1
```
7
ABACABA
```
输出#1
```
AB
```
输入#2
```
5
ZZZAA
```
输出#2
```
ZZ
```

说明/提示

In 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.

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