#include<bits/stdc++.h>

using namespace std;
struct I{I(){ios::sync_with_stdio(false);cin.tie(0);}}init;

int main(){
    int N;cin>>N;
    vector<int> x(N);
    for(auto &it:x)cin>>it;
    sort(x.begin(),x.end());
    int top=1,bottom=1e9;
    for(int i=1;i<N;i++)top=max(top,x[i]-x[i-1]),bottom=min(bottom,x[i]-x[i-1]);
    if(bottom==top)cout<<"YES"<<endl;
    else cout<<"NO"<<endl;
    return 0;
}