#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

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

    if(n >= 4){
        cout << "YES" << endl;
        return 0;
    }

    for(int i=0; i<n-1; ++i){
        if(s[i] == s[i+1]){
            cout << "YES" << endl;
            return 0;
        }
    }

    cout << "NO" << endl;
    return 0;
}