#include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <cassert>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <bitset>
using namespace std;

#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define mp(a,b) make_pair(a,b)
#define pb(a) push_back(a)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define fi first
#define se second

#define INF 2147483600

int main(){
  int n;
  cin>>n;
  vector<int> vec(n);
  rep(i,n) scanf("%d", &vec[i]);

  sort(all(vec));

  int d = vec[1]-vec[0];
  rep(i,n-1){
    int dd=vec[i+1]-vec[i];
    if(dd==0 || dd!=d){
      cout<<"NO"<<endl;
      return 0;
    }
  }
  cout<<"YES"<<endl;

  return 0;
}