#include <iostream>
#include <vector>
#include <algorithm>

#define MAX 100000

int main() {
	std::vector<int> v;
	int n, r, tmp;
	std::cin >> n;

	for (int i = 0; i < n; i++) {
		std::cin >> tmp;
		v.push_back(tmp);
	}

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

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

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

	return 0;
}