#include <bits/stdc++.h>
using namespace std;
vector<int> ball;
int main() {
  int n, x;
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> x;
    if (find(ball.begin(), ball.end(), x) == ball.end()) ball.push_back(x);
  }
  sort(ball.begin(), ball.end());
  for (int i = 0; i < ball.size(); i++) {
    if (ball[i - 2] + 1 == ball[i - 1] && ball[i - 1] + 1 == ball[i]) {
      cout << "YES" << endl;
      return 0;
    }
  }
  cout << "NO" << endl;
  return 0;
}
