#include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <fstream>
#include <set>
#include <utility>
#include <algorithm>

using namespace std;

int max(int x, int y) {
	int a;
	(x > y) ? a = x : a = y;
	return a;
}

int min(int x, int y) {
	int a;
	(x < y) ? a = x : a = y;
	return a;
}

int main() {
	int n;
	cin >> n;
	vector<int> v(n);

	for (int i = 0; i < n; i++)cin >> v[i];

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

	bool judge = true;
	int diff = v[1] - v[0];
	if (diff != 0) {
		for (int i = 1; i < n; i++) {
			if (v[i] - v[i - 1] != diff)judge = false;

		}
	}
	else judge = false;
	if (judge)cout << "YES" << endl;
	else cout << "NO" << endl;

	return 0;
}