#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> vect(n);
  for (int i = 0; i < n; i++) {
    cin >> vect[i];
  }
  sort(vect.begin(), vect.end());
  for (int i = 1; i < n; i++) {
    if (vect[i] - vect[i - 1] != 1) {
      cout << "No" << endl;
      return 0;
    }
  }
  cout << "Yes" << endl;
}
