#include <iostream>
#include <string>

using namespace std;

int main() {
	int n;
	string s;
	cin >> n >> s;
	bool result;
	if (n == 1) {
		result = false;
	} else if (n == 2) {
		result = (s[0] == s[1]);
	} else if (n == 3) {
		result = (s[0] == s[1] || s[1] == s[2]);
	} else {
		result = true;
	}
	cout << (result ? "YES" : "NO") << endl;
	return 0;
}