#include <iostream>
#include <algorithm>
#include <vector>
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());
    bool TF=(x[1]!=x[0]?true:false);
    for(int i=1;i+1<N;i++){
        if(x[i+1]-x[i]!=x[1]-x[0])TF=false;
    }
    cout << (TF?"YES":"NO") << endl;
    return 0;
}