#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;


int main(void) {
	int N; cin >> N;
	string s; cin >> s;
	if (N >= 4) {
		cout << "YES" << endl;
		return 0;
	}
	if (N <= 3) {
		bool f = false;;
		for (int i = 0; i < N-1; ++i) {
			f = (f | (s[i] == s[i + 1]));
		}
		if (f) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}