#include <bits/stdc++.h>
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
using namespace std;
int main() {
  int n;
  cin >> n;
  vector<int> v(n);
  map<int, int> cnt;
  for (int i = 0; i < (int)(n); i++) {
    cin >> v[i];
    if (cnt.find(v[i]) == cnt.end()) cnt[v[i]] = 0;
    cnt[v[i]]++;
  }
  sort((v).begin(), (v).end());
  for (int i = 0; i < (int)(n - 1); i++) {
    if (v[i + 1] - v[i] > 1) {
      cout << "No" << endl;
      return 0;
    }
  }
  vector<int> c;
  for (auto p : cnt) c.push_back(p.second);
  for (int i = 0; i < (int)(c.size()); i++) {
    if (c[i] > 2) {
      cout << "No" << endl;
      return 0;
    }
  }
  cout << "Yes" << endl;
  return 0;
}
