#include <bits/stdc++.h>
using namespace std;
int n, i, j, a[55], k;
bool us[1005] = {false};
int main() {
  cin >> n;
  k = 0;
  for (i = 1; i <= n; ++i) {
    cin >> j;
    if (!us[j]) {
      k++;
      a[k] = j;
    }
    us[j] = 1;
  }
  n = k;
  sort(a + 1, a + n + 1);
  for (i = 1; i <= n - 2; ++i) {
    if (a[i + 1] - a[i] == 1 && a[i + 2] - a[i + 1] == 1) {
      cout << "YES" << endl;
      return 0;
    }
  }
  cout << "NO" << endl;
}
