#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, t[1001];
  for (int i = 0; i <= 1000; i++) {
    t[i] = 0;
  }
  cin >> n;
  for (int i = 0; i < n; i++) {
    int s;
    cin >> s;
    t[s] = 1;
  }
  int count = 0;
  for (int i = 1; i <= 1000; i++) {
    if (t[i] == 0) {
      count = 0;
    } else {
      count++;
    }
    if (count == 3) {
      cout << "YES\n";
      return 0;
    }
  }
  cout << "NO\n";
  return 0;
}
