#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) for(int i = (n) - 1; (i) >= 0; --i)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
#define MOD LL(1e9 + 7)
#define INF 1000000
using namespace std;
typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PI;

int main() {
	int n;
	cin >> n;
	string s;
	cin >> s;
	if (n == 1) {
		cout << "NO" << endl;
		return 0;
	}
	if (n >= 4) {
		cout << "YES" << endl;
		return 0;
	}
	if (s[0] == s[1] || s[1] == s[2])
		cout << "YES" << endl;
	else
		cout << "NO" << endl;
	return 0;
}