#include <iostream>
#include <algorithm>

#define MAX 100000

int main() {
	unsigned int n, a[MAX];
	std::cin >> n;

	for (int i = 0; i < n; i++) {
		std::cin >> a[i];
	}

	std::sort(a, a + MAX);

	int r = a[1] - a[0];
	if (r == 0) {
		std::cout << "NO" << std::endl;
		return 0;
	}

	for (int i = 2; i < n; i++) {
		if ((r != a[i] - a[i - 1]) || (a[i] == a[i - 1])) {
			std::cout << "NO" << std::endl;
			return 0;
		}

		r = a[i] - a[i - 1];
	}

	std::cout << "YES" << std::endl;

	return 0;
}