#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include "bits/stdc++.h"
#define REP(i,a,b) for(i=a;i<b;++i)
#define rep(i,n) REP(i,0,n)
#define ll long long
#define ull unsigned ll
typedef long double ld;
#define ALL(a) begin(a),end(a)
#define ifnot(a) if(not a)
#define dump(x)  cerr << #x << " = " << (x) << endl
using namespace std;

// #define int ll
bool test = 0;
int dx[] = { 0,1,0,-1 };
int dy[] = { 1,0,-1,0 };
#define INF (1 << 28)
ull mod = (int)1e9 + 7;
//.....................
#define MAX (int)1e6 + 5

signed main(void) {
	ll i, j, k, l;
	ll N;
	string s;
	cin >> N >> s;
	if (N > 3) {
		puts("YES");
		return 0;
	}

	rep(i, N) REP(j, i, N) {
		if (j + 1 + (j - i) >= N) continue;
		if (s.substr(i, j - i + 1) == s.substr(j + 1, j - i + 1)) {
			puts("YES");
			return 0;
		}
	}
	puts("NO");
	return 0;
}