#include <bits/stdc++.h>
#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <string>
#include <sstream>
#include <cmath>
#include <stack>
#include <queue>
#include <cctype>
#include <stdio.h>
#include <map>
#include <string.h>
#include <utility>

typedef long long ll;
using namespace std;

typedef pair<int, int> P;


int main() {

	int n=0;
	string s;
	cin>>n>>s;

	if(n>4){
		cout<<"YES"<<endl;
					return 0;
	}

	for(int i=0; i<s.length()-1; i++){
		for(int j=i; j<s.length(); j++){

			string a =s.substr(i,j-i+1);
			if(j+(j+1-i)<s.length()){
/*				cout<<i<<" "<<j<<endl;*/
			string b =s.substr(j+1,j+(j+1-i));

	/*		cout<<a<<" "<<b<<endl;
*/
			if(a == b){
				cout<<"YES"<<endl;
				return 0;

			}
			}

		}
	}

	cout<<"NO"<<endl;

	return 0;
}