#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> t(n, 0);
  for (int i = 0; i < n; ++i) {
    cin >> t[i];
  }
  sort(t.begin(), t.end());
  auto last = unique(t.begin(), t.end());
  t.erase(last, t.end());
  n = t.size();
  for (int i = 0; i < n - 2; i++) {
    if (t[i + 2] - t[i] < 3) {
      cout << "YES";
      return 0;
    }
  }
  cout << "NO";
  return 0;
}
