#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a[n], s[1001] = {0};
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    s[a[i]] = 1;
  }
  for (int i = 0; i <= 998; i++) {
    if (s[i] && s[i + 1] && s[i + 2]) {
      cout << "YES";
      return 0;
    }
  }
  cout << "NO";
}
