#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll mod = 1e9 + 7;
const ll inf = (1 << 30) - 1;
const ll infll = (1LL << 61) - 1;

int n, d;

int main()
{
    cin >> n;
    vector<int> a;
    for (int i = 0; i < n; i++)
    {
        int p;
        cin >> p;
        a.push_back(p);
    }
    bool f = 1;
    sort(a.begin(), a.end());
    d = a[1] - a[0];
    for (int i = 2; i < n; i++)
    {
        if (a[i - 1] + d!= a[i])
            f = false;
    }

    cout << (f ? "YES" : "NO") << endl;
}