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

int main() {
	int n;
	cin >> n;

	vector<int> a(n);
	for (int i = 0; i < n; i++) {
		scanf("%d", &a[i]);
	}
	sort(a.begin(), a.end());

	int mini = 1e9, maxi = -1e9;
	for (int i = 0; i < n - 1; i++) {
		mini = min(mini, a[i + 1] - a[i]);
		maxi = max(maxi, a[i + 1] - a[i]);
	}

	if (mini == maxi && maxi != 0) {
		cout << "YES" << endl;
	} else {
		cout << "NO" << endl;
	}
}