#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int main() {
  int n, b, c;
  bool f = true;
  cin >> n;
  vector<int> a(n);
  for (auto& e : a) cin >> e;
  sort(a.begin(), a.end());
  int d = a[1] - a[0];
  for (int i = 1; i < n - 1; i++) {
    if (a[i + 1] - a[i] != d) {
      f = false;
      break;
    }
  }
  if (d && f) cout << "YES" << endl;
  else cout << "NO" << endl;
}