#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  long long t;
  cin >> t;
  long long arr[1001] = {0};
  long long temp;
  for (long long i = 0; i < t; ++i) {
    cin >> temp;
    arr[temp]++;
  }
  for (int i = 1; i <= 999; ++i) {
    if (arr[i] > 0 and arr[i - 1] > 0 and arr[i + 1] > 0) {
      cout << "YES\n";
      return 0;
    }
  }
  cout << "NO\n";
  return 0;
}
