#include <bits/stdc++.h>

using namespace std;

struct Initializer {
  Initializer() {
    cin.tie(0);
    ios::sync_with_stdio(0);
    cout << fixed << setprecision(15);
  }
} initializer;

int main() {
  int n;
  string s;
  cin >> n >> s;
  cout << (n >= 4 || s.find("00") != string::npos || s.find("11") != string::npos ? "YES" : "NO") << endl;
}