#include <bits/stdc++.h>

using namespace std;

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

  int sz = s.size();
  bool yes = false;
  for (int i = 0; i + 1 < sz; i++) {
    if (s[i + 1] == s[i]) {
      yes = true;
    } else if (i + 3 < sz && s.substr(i, 2) == s.substr(i + 2, 2)) {
      yes = true;
    }
  }
  cout << (yes ? "YES" : "NO") << endl;

  return 0;
}