#include <bits/stdc++.h>
using namespace std;
const int N = 200005;
int a[N];
int main() {
  ios::sync_with_stdio(0);
  int n;
  cin >> n;
  int x;
  for (int(i) = (0); i < (n); ++(i)) {
    cin >> x;
    a[x] = 1;
  }
  for (int(i) = (0); i < (10000); ++(i))
    if (a[i] && a[i + 1] && a[i + 2]) {
      cout << "YES";
      return 0;
    }
  cout << "NO";
}
