#define _USE_MATH_DEFINES
#include  <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include<math.h>
#include<iomanip>
#include<stdio.h>
#include <stdlib.h>
#include<stdio.h>
#include <queue>
#include<map>
#include <fstream>
#include <sstream>
#include<set>
#include<stack>
#include<time.h>
#include <sys/types.h>
#include <tuple>
#include <numeric>
#include <iterator>

typedef long long int ll;
//#include<bits/stdc++.h>


using namespace std;





int main()
{

    int Q;
    Q = 1;
    //cin >> Q;


    while (Q--) {
       
        int n;
        cin >> n;
        vector<int>a(n);
        for (int i = 0; i < n; i++)cin >> a[i];

        sort(a.begin(), a.end());
        set<int>s;
        for (int i = 0; i < n - 1; i++) {
            int x = a[i + 1] - a[i];
            if (!x) {
                cout << "NO"; return 0;
            }
            s.insert(x);
        }
        if (s.size() > 1)cout << "NO";
        else cout << "YES";
        
    }
    return 0;
}