#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main(){
    vector<int> V;
    int N;
    cin>>N;
    for(int i=0;i<N;i++){
        int x;
        cin>>x;
        V.push_back(x);
    }
    sort(V.begin(),V.end());
    int l=V[1]-V[0];
    for(int i=2;i<N;i++){
        if(V[i]-V[i-1]==l) continue;
        else{
            cout<<"NO"<<endl;
            return 0;
        }
    }
    cout<<(l?"YES":"NO")<<endl;
    return 0;
}