#include <bits/stdc++.h>
using namespace std;
int a[100000];
int main() {
  int n;
  cin >> n;
  for (int i = 0, x; i < n; i++) cin >> x, a[x] = 1;
  for (int i = 0; i < 10000; i++)
    if (a[i] && a[i + 1] && a[i + 2]) return cout << "YES", 0;
  cout << "NO";
}
