#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  bool yes = 0;
  int a;
  set<int> x;
  for (int i = 0; i < n; i++) cin >> a, x.insert(a);
  set<int>::iterator it;
  int num1, num2, num3;
  for (it = x.begin(); it != x.end(); it++) {
    if (it == x.begin())
      num1 = *it;
    else if (!yes)
      num2 = *it, yes = 1;
    else {
      num3 = *it;
      if (num3 - num2 == 1 && num2 - num1 == 1) {
        cout << "YES";
        return 0;
      } else
        num1 = num2, num2 = num3;
    }
  }
  cout << "NO";
  return 0;
}
