#define _GLIBCXX_DEBUG
#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];
  if(diff != 0){
    for(int i = 2; i < N; i++){
      if(X[i]-X[i-1] != diff){
        cout << "NO" << endl;
        return 0;
      }
    }
    cout << "YES" << endl;
  }else{
    cout << "NO" << endl;
  }
}