#include<iostream>
#include<string>

using namespace std;

int main(){

	int N;
	string S;

	cin>>N;
	cin>>S;

	for(int i=1;i<=N;i++){
		for(int j=i;j<=N;j++){
			if(S.substr(i-1,j-1-(i-1)+1)==S.substr(j,j+(j+1-i)-j)){
				cout<<"YES"<<endl;
				return 0;
			}
		}
	}

	cout<<"NO"<<endl;
}