#include <bits/stdc++.h>
using namespace std;
const int inf = 10e8;
int main() {
  int n;
  cin >> n;
  vector<int> g(n);
  vector<int> sor(1005, 0);
  for (int i = 0; i < n; i++) {
    cin >> g[i];
    sor[g[i]]++;
  }
  for (int i = 0; i < 1000; i++) {
    if (sor[i] != 0 && sor[i + 1] != 0 && sor[i + 2] != 0) {
      cout << "YES";
      return 0;
    }
  }
  cout << "NO";
  return 0;
}
