#include <bits/stdc++.h>
using namespace std;
int main() {
  int Z = 0;
  int i = 0, j = 0, k = 0;
  int n = 0;
  int in = 0;
  int flag = 0;
  int nums[100000];
  vector<int> vnums;
  cin >> n;
  for (i = 0; i < n; i++) {
    cin >> in;
    vnums.emplace_back(in);
  }
  sort(vnums.begin(), vnums.end());
  for (i = 1; i < n; i++) {
    if (vnums[i] - vnums[i - 1] != 1) {
      cout << "No" << endl;
      flag = 1;
      break;
    }
  }
  if (flag == 0) {
    cout << "Yes" << endl;
  }
  return 0;
}
