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

using namespace std;
using ll = long long;

int main() {
    int n;
    string s;
    cin >> n >> s;

    bool contains = false;
    for (int i = 0; i < n - 1; i++) {
        if (s[i] == s[i + 1])contains = true;
    }

    if (n >= 4 || contains)cout << "YES" << endl;
    else cout << "NO" << endl;
    return 0;
}