#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;

int main() {
    
    int N;
    cin >> N;
    string S;
    cin >> S;
    for ( int i = 0; i < N-1; i++ ) {
        if ( S[i] == S[i+1] ) { cout << "YES" << endl; return 0; }
    }
    cout << "NO" << endl;
    
    return 0;
}