#include <iostream>
#include <vector>
#include <algorithm>
#include <array>
#include <set>
#include <map>
#include <queue>
#include <tuple>
#include <unordered_set>
#include <unordered_map>
#include <functional>
#include <cstdio>
#include <cassert>
#define repeat(i,n) for (int i = 0; (i) < (n); ++(i))
#define repeat_from(i,m,n) for (int i = (m); (i) < (n); ++(i))
using namespace std;
int main() {
    int n; cin >> n;
    string s; cin >> s;
    repeat (i,n) {
        repeat_from (j,i,n) {
            int l = j-i+1;
            if (j + l < n) {
                if (s.substr(i, l) == s.substr(j+1, l)) {
                    cout << "YES" << endl;
                    return 0;
                }
            }
        }
    }
    cout << "NO" << endl;
    return 0;
}