#include <iostream>
#include <string>
using namespace std;
string Substr(string S,int s,int e)
{
	string S1;
	for (int i=s-1;i<=e-1;i++){
		S1+=S[i];
	}
	return S1;
}
int main(int argc, char* argv[])
{
	int N;
	string S;
	cin>>N;
	cin>>S;
	int i,j;
	for (i=1;i<N;i++){
		for (j=i;j<N;j++){
			if (j+(j+1-i)<=N){
				string S1=Substr(S,i,j);
				string S2=Substr(S,j+1,j+(j+1-i));
				if (!S1.compare(S2)){
					cout<<"YES"<<endl;
					return 0;
				}
			}
		}
	}
	cout<<"NO"<<endl;
	return 0;
}