#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(){
    int n;cin>>n;
    vector<int> a(n);
    for(int i = 0; n > i; i++){
        cin>>a[i];
    }
    sort(a.begin(),a.end());
    int k = 0;
    for(int i = 1; n > i; i++){
        if(!(a[i]-a[i-1])){
            cout << "NO" << endl;
            return 0;
        }
        if(i==1){
            k = a[i]-a[i-1];
        }else if(k != a[i]-a[i-1]){
            cout << "NO" << endl;
            return 0;
        }
    }
    cout << "YES" << endl;
}