#define _USE_MATH_DEFINES
 
#include <iostream>
#include <iomanip>
#include <sstream>
 
#include <algorithm>
#include <cmath>
 
#include <string>
#include <queue>
#include <vector>
#include <complex>
#include <set>
#include <map>
#include <stack>
#include <list>
 
/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
 
#define PII pair<int,int>
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////

void solve(){
	int N;
	string str;
	cin >> N;
	if( N >= 4 ){
		cout << "YES\n";
	}

	cin >> str;
	int h,i,k;
	bool flag;
	for(h = 0; h < N/2; ++h){
		for(i=0; i+2*h+1 < N; ++i ){
			flag = true;
			for(k=0;k <= h; ++k){
				if( str[i+k] != str[i+h+1+k] ){
					i = i + k;
					flag = false;
					break;
				}
			}
			if( flag ){
				cout << "YES\n";
				return;
			}
		}
	}
	cout << "NO\n";
	return;
}

int main(void){
    std::cin.tie(0); 
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//
    //cout << setprecision(16);//
	
	//cpp
	solve();
	return 0;
}