#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, f = 0;
  cin >> n;
  int i;
  int j;
  set<int> t;
  for (i = 0; i < n; i++) {
    cin >> j;
    t.insert(j);
  }
  vector<int> v;
  for (auto i : t) v.push_back(i);
  for (i = 2; i < v.size(); i++) {
    if ((v[i] - 1 == v[i - 1]) && (v[i - 1] - 1 == v[i - 2])) {
      f = 1;
      break;
    }
  }
  if (f == 1)
    cout << "YES";
  else
    cout << "NO";
}
