#include <iostream>
#include <algorithm>
#include <string>
#include <cstdio>
using namespace std;

int main()
{
    int n;
    cin >> n;

    int a[n];
    for (auto& x : a) cin >> x;

    sort(a, a + n);

    int d;
    for (int i = 0; i < n - 1; i++) {
        if (a[i] == a[i + 1]) return cout << "NO\n", 0;
        if (!i) d = a[i + 1] - a[i];
        if (a[i + 1] - a[i] != d) return cout << "NO\n", 0;
    }
    cout << "YES\n";

    return 0;
}