#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#define vll vector<ll>
#define vvvl vector<vvl>
#define vvl vector<vector<ll>>
#define VV(a, b, c, d) vector<vector<d>>(a, vector<d>(b, c))
#define VVV(a, b, c, d) vector<vvl>(a, vvl(b, vll (c, d)));
#define re(c, b) for(ll c=0;c<b;c++)
#define all(obj) (obj).begin(), (obj).end()
typedef long long int ll;
typedef long double ld;
using namespace std;

int main(int argc, char const *argv[]) {
  ll n;std::cin >> n;
  vll a(n);re(i, n) std::cin >> a[i];
  if(n==1) std::cout << "YES" << '\n';
  else{
    sort(all(a));
    ll sa = a[1] - a[0];
    if(sa==0) std::cout << "NO" << '\n';
    else{
      for(int i=2;i<n;i++){
        if(a[i]-a[i-1]!=sa||a[i]-a[i-1]==0){
          std::cout << "NO" << '\n';
          return 0;
        }
      }
      std::cout << "YES" << '\n';
    }
  }
}