#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cctype>
#include<cstdlib>
#include<algorithm>
#include<bitset>
#include<vector>
#include<list>
#include<deque>
#include<queue>
#include<map>
#include<set>
#include<stack>
#include<cmath>
#include<sstream>
#include<fstream>
#include<iomanip>
#include<ctime>
#include<complex>
#include<functional>
#include<climits>
#include<cassert>
#include<iterator>
using namespace std;
int n;
string S;
string ss;
char s[1000002];
int main() {
	scanf("%d", &n);
	scanf("%s", s);
	//string ss = s;
	ss = s;
	for (int k = 1;k <= ss.size()&&clock()/(double)(CLOCKS_PER_SEC)<4.8;k++) {
		for (int i = 0;i < ss.size()&&clock()/(double)(CLOCKS_PER_SEC)<4.8;i++) {
			if (i + k * 2 > ss.size()) {
				break;
			}
			S = ss.substr(i, k);
			if (S == ss.substr(i+k, k)) {
				puts("YES");
				return 0;
			}
		}
	}
	puts("NO");
	return 0;
}