#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <stack>
#include <algorithm>
#include <string>
#include <map>
#include <iterator>
#include <set>
#include <queue>

using namespace std;


int main() {

    int N;
    cin >> N;
    vector<long> xs;
    for (int i = 0; i < N; ++i) {
        long x;
        cin >> x;
        xs.push_back(x);
    }

    sort(xs.begin(), xs.end());

    long interval = xs[1] - xs[0];
    string result = "YES";
    if (interval == 0) {
        result = "NO";
    } else {

        for (int i = 1; i < N - 1; ++i) {
            if (interval != (xs[i + 1] - xs[i])) {
                result = "NO";
                break;
            }
        }
    }

    cout << result << endl;

    return 0;
}