#include <bits/stdc++.h>
using namespace std;

int main() {
  int n;
  vector<int64_t> xs(n);
  for (int i = 0; i < n; i++) {
    cin >> xs[i];
  }
  sort(xs.begin(), xs.end());
  bool flag = true;
  int64_t sa = abs(xs[1] - xs[0]); 
  for (int i = 1; i < n - 1; i++) {
    if (abs(xs[i] - xs[i + 1]) != sa) {
      flag = false;
      break;
    }
  }
  if (flag) cout << "YES" << endl;
  else cout << "NO" << endl;
  return 0;
}