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

#define INT(n) int n; scanf("%d",&n);
#define VI(v,n) vector<int> v(n); for(int i=0;i<n;i++){scanf("%d",&v[i]);}
#define FOR(var,a,b) for(int var=(a);var<(b);var++)
#define SZ(a) int((a).size())
#define SORT(c) sort((c).begin(),(c).end())

int main(){
  INT(n); VI(xs, n);
  SORT(xs);
  string ans = "YES";
  int dif = xs[1] - xs[0];
  FOR(i, 2, SZ(xs)){
    if (xs[i] - xs[i - 1] != dif){
      ans = "NO";
      break;
    }
  }
  cout << ans << endl;
  return 0;
}