#include "bits/stdc++.h"
using namespace std;

#define REP(i, n) for(int i=0; i<(n); i++)

int N,T;
string S;
signed main()
{
    cin >> N >> S;
    if (N == 1) {
        cout << "NO" << endl;
        return 0;
    }
    if (N >= 4) {
        cout << "YES" << endl;
        return 0;
    }
    int prev = -1;
    for (auto&& t : S) {
        if (t == prev) {
            cout << "YES" << endl;
            return 0;
        }
        prev = t;
    }
    cout << "NO" << endl;
    return 0;
}