#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n,s,flug=0;
    cin>>n;
    vector<int> x(n);
    for(int i=0;i<n;i++)cin>>x[i];
    sort(x.begin(),x.end());
    s=abs(x[0]-x[1]);
    if(s!=0){
        for(int i=0;i<n-1;i++){
            if(abs(x[i]-x[i+1])!=s)flug=1;
        }
    }else flug=1;
    if(flug==0)cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
    return 0;
}