#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll =  long long ;
using P = pair<int,int> ;
using pll = pair<ll,ll>;
constexpr int INF = 1e9;
constexpr ll LINF = 1e18;
constexpr int MOD = 1000000007;

int main(){
    int n;
    cin >> n;
    string s;
    cin >> s;
    bool ok = false;
    if(n >= 4) ok = true;
    else if(n==1) ok = false;
    else if(n==2){
        if(s[0] == s[1]) ok = true;
    }
    else{
        if(s[0] == s[2] && s[0] != s[1]);
        else ok = true;
    }
    cout << (ok ? "YES" : "NO") << endl;
    return 0;
}