#include <bits/stdc++.h>
using namespace std;
const int SIZE = 1e3 + 5;
int main() {
  int n, t, arr[SIZE];
  memset(arr, 0, sizeof(arr));
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> t;
    arr[t] = 1;
  }
  for (int i = 3; i <= 1000; i++)
    if (arr[i - 2] && arr[i - 1] && arr[i]) return printf("YES\n") * 0;
  cout << "NO" << endl;
  return 0;
}
