#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(LL i = a;i<b; i++)
#define rrep(i,a,b) for(LL i = a;i>b; i--)
#define INF ((1LL<<62)-(1LL<<31))
#define ooki 9,223,372,036,854,775,807
#define tii -9,223,372,036,854,775,808
typedef long long LL;
int main(){
 LL n;
  cin >> n;
  set<LL> s;
  vector<LL> x(n);
  rep(i,0,n){cin>>x[i];s.insert(x[i]);}
  if(s.size()!=n){cout<<"NO"<<endl;return 0;}
  sort(x.begin(),x.end());
  LL a = x[1]-x[0];
  rep(i,0,n-1){
    if(x[i+1]-x[i]!=a){cout<<"NO"<<endl;return 0;}
  }
  cout << "YES" << endl;
}