#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <list>

using namespace std;

typedef long long ll;

#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(ll i=(a);i<(b);++i)
#define clr(a, b) memset((a), (b) ,sizeof(a))
#define ctos(d) string(1,d)
#define print(x) cout<<#x<<" = "<<x<<endl;

#define MOD 1000000007

int main() {
  ll n;
  cin>>n;
  vector<ll> v;
  rep(i,0,n){
  	ll a;
  	cin>>a;
  	v.pb(a);
  }
  sort(all(v));
  ll d = v[1]-v[0];
  int flag = 1;
  rep(i,2,n){
  	if(v[i]-v[i-1]!=d)flag = 0;
  }
  if(d!=0 && flag == 1)cout << "YES" << endl;
  else cout << "NO" << endl;
  return 0;
}