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

using namespace std;

int main(int argc, const char* argv[])
{
	int N;
	cin >> N;
	vector<size_t> xs(N);
	for (auto&& x : xs) {
		cin >> x;
	}
	sort(xs.begin(), xs.end());

	size_t gap = xs[1] - xs[0];
	if (gap == 0) {
		cout << "NO" << endl;
		return 0;
	}
	for (int i = 1; i < N; i++) {
		if (xs[i] - xs[i - 1] != gap) {
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
	return 0;
}