#include <bits/stdc++.h>
using namespace std;
int n, temp, k = 0, input[1001], a[1001];
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> temp;
    a[temp]++;
    if (a[temp] == 1) input[k++] = temp;
  }
  sort(input, input + k);
  for (int i = 2; i < k; i++) {
    if (input[i] - input[i - 2] == 2 && input[i - 1] == input[i - 2] + 1) {
      cout << "YES";
      return 0;
    }
  }
  cout << "NO";
}
