#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <stack>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;

int main(){
  ios::sync_with_stdio(false);
  int N;
  vector<ll> v;
  cin >> N;
  rep(i,N){
    ll x;
    cin >> x;
    v.push_back(x);
  }
  sort(ALLOF(v));
  int p = v[1] - v[0];
  if(p==0){
    cout << "NO" << endl;
    return 0;
  }
  REP(i,1,N){
    if(v[i-1]+p != v[i]){
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
}