#include <bits/stdc++.h>
using namespace std;
int b[1005], a[1000];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    b[a[i]]++;
  }
  for (int i = 1; i <= 1000; i++) {
    if (b[i] && b[i + 1] && b[i + 2]) {
      cout << "YES" << endl;
      return 0;
    }
  }
  cout << "NO" << endl;
  return 0;
}
