#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.at(i);
  sort(X.begin(), X.end());
  int tmp = X.at(1) - X.at(0);
  string ans = "YES";
  for (int i = 1; i < N; i++)
    if (X.at(i) - X.at(i - 1) != tmp) ans = "NO";
  cout << ((tmp) ? ans : "NO") << "\n";
}