#include<iostream>
#include<vector>
#include<string>
#include<cstdio>
#include<algorithm>
using namespace std;
int main(){
    long int N,x,a,flag=0;
    vector<long int> num;
    cin >> N;
    while(N--){
        cin >> x;
        num.push_back(x);
    }
    sort(num.begin(),num.end());
    a = num[1]-num[0];
    for(int i=1;i<num.size()-1;i++){
        if(a != num[i+1]-num[i]){
            flag++;
            break;
        }
        a = num[i+1]-num[i];
    }
    if(flag)    cout << "NO";
    else    cout << "YES";
    return 0;
}