#include<iostream>
#include<vector>
#include<algorithm>
#define rep(i,n) for(i=0; i<n; i++)
#define rep2(i,a,b) for(i=a; i<b; i++)
using namespace std;

int vector_check(vector<int> v)
{
  int i, j;
  rep(i,v.size()) {
    rep2(j,i+1,v.size()) {
        if(v[i]==v[j]) { return 0; }
        else continue;
    }
  }
  return 1;
}

void end_NO ()
{
    cout << "NO" << endl;
}

int main()
{
    int n;
    cin>>n;
    vector<int> v(n);
    int i,num;
    rep(i,n) {
        cin>>num;
        v[i] = num;
    }
    
    sort(v.begin(), v.end());
    
    if(vector_check(v) == 0) { end_NO(); return 0; }
    
    rep(i,v.size()-1) {
        if(i==0) { num = v[i+1] - v[i]; }
        else if(i>=1) {
            if(num!=v[i+1]-v[i]) { end_NO(); return 0; }
        }
    }
    

    cout << "YES" << endl;
     
    return 0;
}