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

int main() {
    int n;
    cin >> n;
    vector<int> a(n);
    for (int &e : a) cin >> e;
    
    sort(a.begin(), a.end());
    
    const int d = a[1] - a[0];
    bool ok = (d > 0);
    
    for (int i = 1; i + 1 < n; i++) {
        ok &= (d == a[i+1] - a[i]);
    }
    
    cout << (ok ? "YES" : "NO") << '\n';
    return 0;
}