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