#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define RFOR(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define REP(i, n) for (int i = 0; i < (n); i++)
#define RREP(i, n) for (int i = (n)-1; i >= 0; i--)
#define MIN(a, b) (a > b ? b : a)
#define MAX(a, b) (a > b ? a : b)

#include <bits/stdc++.h>

using namespace std;

int N;
string S;

void solve() {
    cin >> N >> S;

    if (N == 1) {
        cout << "NO" << endl;
    }
    else if (N == 2) {
        cout << (S[0] == S[1] ? "YES" : "NO") << endl;
    }
    else if (N == 3) {
        cout << (S[0] == S[1] || S[1] == S[2] ? "YES" : "NO") << endl;
    }
    else if (N >= 4) {
        cout << "YES" << endl;
    }
}

int main() {
    solve();
    return 0;
}