#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
ld pie=3.141592653589793;
ll inf=1444440099999944;
ll mod=1000000007;
int main(){
    ll n;
    cin >> n;
    string s;
    cin >> s;
    if (n>=4)
    {
        cout << "YES" << endl;
    }else{
        if (n==1)
        {
            cout << "NO" << endl;
        }else if (n==2)
        {
            if (s[0]==s[1])
            {
                cout << "YES" << endl;
            }else{
                cout << "NO" << endl;
            }
        }else{
            if (s[0]==s[2]&&s[0]!=s[1])
            {
                cout << "NO" << endl;
            }else{
                cout << "YES" << endl;
            }
            
        }
    }
    
}