#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> t;
  int x;
  for (int i = 0; i < n; i++) {
    cin >> x, t.push_back(x);
  }
  for (int i = 0; i < n; i++) {
    for (int j = i + 1; j < n; j++) {
      for (int k = j + 1; k < n; k++) {
        if (t[i] != t[j] && t[j] != t[k] && t[i] != t[k] &&
            max(t[i], max(t[j], t[k])) - min(t[i], min(t[j], t[k])) <= 2) {
          cout << "YES" << endl;
          return 0;
        }
      }
    }
  }
  cout << "NO" << endl;
  return 0;
}
