#include <bits/stdc++.h>
using namespace std;

int main() {
	int n;
	string s;
	cin >> n >> s;

	for (int i = 0;i < n;i++) {
		for (int j = i;j+(j+1-i)<n;j++) {
			bool b = true;
			for (int k = 0;k <= j - i;k++) {
				if(s[i+k]!=s[j+1+k]){
					b = false;
				}
			}
			if (b) {
				cout << "YES" << endl;
				return 0;
			}
		}
	}
	cout << "NO" << endl;



	return 0;
}