#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  vector<int> x;
  cin >> n;
  for (int i = 0; i < n; i++) {
    int t;
    cin >> t;
    x.push_back(t);
  }
  int b1, b2, b3;
  for (int i = 0; i < n; i++) {
    b1 = x[i];
    for (int j = i + 1; j < n; j++) {
      b2 = x[j];
      for (int k = j + 1; k < n; k++) {
        b3 = x[k];
        if (abs(b1 - b2) <= 2 && abs(b1 - b3) <= 2 && abs(b2 - b3) <= 2 &&
            b1 != b2 && b1 != b3 && b2 != b3) {
          cout << "YES" << endl;
          return 0;
        }
      }
    }
  }
  cout << "NO" << endl;
  return 0;
}
