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

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