#include <bits/stdc++.h>
using namespace std;
int a[1005];
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  n = unique(a, a + n) - a;
  for (int i = 2; i < n; i++)
    if (a[i] - a[i - 2] == 2) {
      cout << "YES\n";
      return 0;
    }
  cout << "NO\n";
  return 0;
}
