#include <iostream>
#include <math.h>
#include <algorithm>
#include <functional>
#include <vector>
#include <typeinfo>
#include <climits>
#include <ctype.h>
#include <string>
#include <stdio.h>
using namespace std;
#define INIT cin.tie(0); ios::sync_with_stdio(false);
#define FOR(i, a, n) for (int i = a; i < n; i++)
#define REP(i, n) for(int i = 0; i < n; i++)

int main()
{
    INIT;

    int n;
    cin >> n;

    int A[n];
    REP(i, n) cin >> A[i];
    sort(A, A + n);

    int d1, d2, f = 1;
    REP(i, n - 1){
        if(A[i] == A[i + 1]){
            f = 0;
            break;
        }
        if(i == 0) d1 = A[i + 1] - A[i];
        else{
            d2 = A[i + 1] - A[i];
            if(d1 != d2){
                f = 0;
                break;
            }
        }
    }
    if(f == 0) cout << "NO" << endl;
    else cout << "YES" << endl;

    return 0;
}