#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int v[51];
  for (int i = 0; i < n; i++) cin >> v[i];
  bool yes = false;
  for (int i = 0; i < n; i++) {
    for (int j = i + 1; j < n; j++) {
      for (int k = j + 1; k < n; k++) {
        if (abs(v[i] - v[j]) <= 2 && abs(v[j] - v[k]) <= 2 &&
            abs(v[i] - v[k]) <= 2) {
          if (v[i] != v[j] && v[j] != v[k] && v[k] != v[i]) yes = true;
        }
      }
    }
  }
  if (yes)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
}
