#include <iostream>
using namespace std;

int main(){
   int n;
   string s;
   cin >> n >> s;
   if(n > 3) cout << "YES" << endl;
   else if(s == "010" || s == "101" || s == "01" || s == "10" || s.size() == 1) cout << "NO" << endl;
   else cout << "YES" << endl;
}