#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  int a[10000];
  int b[1009] = {0};
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    b[a[i]] = 1;
  }
  sort(a, a + n);
  for (int i = 0; i < 1009; i++) {
    if (b[i] && b[i + 1] && b[i + 2]) {
      cout << "YES";
      return 0;
    }
  }
  cout << "NO";
  return 0;
}
