#include <algorithm>
#include <iostream>
#include <numeric>
#include <string>
#include <utility>
#include <vector>

int main() {
  int n;
  int x[100000];
  std::cin >> n;
  for (int ni = 0; ni < n; ++ni) {
    std::cin >> x[ni];
  }
  std::sort(x, x + n);
  for (int ni = 0; ni < n - 1; ++ni) {
    if (x[1] - x[0] == 0 or x[1] - x[0] != x[ni + 1] - x[ni]) {
      std::cout << "NO" << std::endl;
      return 0;
    }
  }
  std::cout << "YES" << std::endl;
  return 0;
}