#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    vector<int> v;
    
    cin >> n;
    
    int tmp;
    for (int i = 0; i < n; i++) {
        cin >> tmp;
        v.push_back(tmp);
    }
    
    sort(v.begin(), v.end());
    
    int dist = v[1] - v[0];
    for (int i = 0; i < n - 1; i++) {
        if (dist == 0 ||
            dist != v[i + 1] - v[i]) {
            cout << "NO" << endl;
            return 0;
        }
    }
    
    cout << "YES" << endl;
    
    return 0;
}