#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
  }
  sort(a.begin(), a.end());
  bool ok = true;
  int cur = -1;
  int q = 0;
  for (int i = 0; i < n; ++i) {
    if (q == 0) {
      if (cur != -1 && a[i] != a[i - 1]) {
        ok = false;
        break;
      }
      q = 1;
      cur = a[i];
    } else {
      if (cur == a[i]) {
        ++q;
      } else {
        if (cur == a[i] - 1) {
          --q;
        } else {
          ok = false;
          break;
        }
      }
    }
  }
  ok &= q == 0;
  if (ok) {
    cout << "YES\n";
  } else {
    cout << "NO\n";
  }
  return 0;
}
