#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  int i;
  int k;
  int a[1005] = {0};
  cin >> n;
  for (i = 0; i < n; i++) {
    cin >> k;
    a[k] = 1;
    if ((k > 1 && k < 1000 && a[k - 1] == 1 && a[k + 1] == 1) ||
        (k > 2 && a[k - 2] == 1 && a[k - 1] == 1) ||
        (k < 999 && a[k + 1] == 1 && a[k + 2] == 1)) {
      cout << "YES";
      return 0;
    }
  }
  cout << "NO";
  return 0;
}
