#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

int main(){
    int n;cin>>n;
    vector<int>x(n);
    for(int i=0;i<n;i++)cin>>x[i];
    sort(x.begin(),x.end());
    int sub=x[1]-x[0];
    for(int i=2;i<n;i++){
        int m=x[i]-x[i-1];
        if(sub!=m) sub=0;
    }
    if(sub)cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
    return 0;
}