#include <bits/stdc++.h>

using namespace std;

int main() {
  int n;
  cin >> n;
  vector<int> x(n);
  for (int i = 0; i < n; ++i) cin >> x[i];
  sort(x.begin(), x.end());
  int diff = x[1] - x[0];
  bool good = true;
  for (int i = 2; i < n; ++i) {
    if (x[i] - x[i - 1] != diff) good = false;
  }

  if (good && diff != 0) puts("YES");
  else puts("NO");
  return 0;
  
}