#include <bits/stdc++.h>
#define rep(i,n) for (int i=0; i<(n); ++i)
using namespace std;
using ll=long long;
int main(){
    int n;
    cin>>n;
    vector<int>x(n);
    rep(i,n){
        cin>>x[i];
    }
    sort(x.rbegin(),x.rend());
    int a=x[0]-x[1];
    rep(i,n-1){
        if(a!=x[i]-x[i+1]){
            cout<<"NO"<<endl;
            return 0;
        }
        else if(x[i]-x[i+1]==0){
            cout<<"NO"<<endl;
            return 0;
        }
    }
    cout<<"YES"<<endl;
}