#include <bits/stdc++.h>
using namespace std;

const int N = (int) 1e5;
int x[N];

int main() {
    ios::sync_with_stdio(false);
    int n; cin >> n;
    for (int i = 0; i < n; ++i) cin >> x[i];
    sort(x, x + n);
    for (int i = 0; i + 1 < n; ++i) if (x[i + 1] - x[i] != x[1] - x[0])
        return cout << "NO\n", 0;
    cout << (x[0] == x[1] ? "NO" : "YES") << endl;
    return 0;
}