包AC

#include<queue>
#include<math.h>
#include<stdio.h>
#include<iostream>
#include<vector>
#include<iomanip>
#include<string.h>
#include<algorithm>
#include<cmath>
#include<cstdio>
#include<cstring>
#include<stack>
#include<fstream>
#include<string>
using namespace std;
#define LL long long
const int N = 1e5 + 10;
const int INF = 0x3f3f3f3f;
int main()
{
    char a[1500];
    int n , cnt = 1;
    cin >> n >> a;
    if ( n == 1) {
    cout << a[0] << endl;
return 0;
}
for(int i=1;i<=strlen(a);i++){
    cin>>a[i];
    if(a[i]==a[i-1]){
        cnt++;
    }
    else cnt=1;
    if(cnt==n){
        cout<<a[i];
        return 0;
    }
}
cout<<"No";
    return 0;
    }