#include <bits/stdc++.h>
#include<iostream>
#include<iomanip>
#include<string>
#include<algorithm>
#include<vector>
#include<set>
#include<list>
#include<queue>
#include<math.h>
#include<bitset>
using ll = long long;
using namespace std;

int main()
{
    ll n;
    string s;
    cin >> n >> s;
    for (int i = 0; i < n - 1; i++){
        for (int j = i; 2*j < n+i-1; j++){
            bool yes = true;
            for (int k = 0; k < j - i + 1; k++){
                if (s[i+k] != s[j+1+k]) {
                    yes = false;
                    break;
                }
            }
            if (yes) {
                cout << "YES" << endl;
                return 0;
            }
        }
    }
    cout << "NO" << endl;
}