#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k, i, max = 0;
  cin >> n;
  int arr[1001] = {0};
  for (i = 1; i <= n; i++) {
    cin >> k;
    arr[k]++;
    if (k > max) max = k;
  }
  for (i = 1; i <= max - 2; i++) {
    if ((arr[i] != 0) && (arr[i + 1] != 0) && (arr[i + 2] != 0)) {
      cout << "YES";
      return 0;
    }
  }
  cout << "NO";
  return 0;
}
