B. Two-gram

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.

Input

The first line of the input contains integer number n (2≤n≤100) — the length of string s. The second line of the input contains the string s consisting of n capital Latin letters.

Output

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.

Examples

input
7
ABACABA
output
AB

input
5
ZZZAA
output
ZZ

Note

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.

這道題就是找給定字串中的長度為2的連續子串出現的次數

str.substr(i,j) 從下標 i 開始，生成長度為 j 的子串
遍歷map的時候需要

map<string,int> ma;
for(map<string,int>::iterator it = ma.begin(); it!=ma.end();++it)
{
	cout<<it->first;
	cout<<" "<<it->second<<endl;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
	string str;
	map<string,int> ma;
	int len;
	cin>>len>>str;
	for(int i=0;i<len-1;++i)
		ma[str.substr(i,2)]++;//str.substr(i,j)  從下標 i 開始，生成長度為 j 的子串 
	string ans;
	int x = 0;
	for(map<string,int>::iterator it = ma.begin(); it!=ma.end();++it)
	{
		if(it->second>=x)
		{
			x = it->second;
			ans = it->first;
		}
	}
	cout<<ans<<endl;
	return 0;
}