#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int main() {
	cin.tie(0);ios::sync_with_stdio(false);
	int N; cin >> N;
	unsigned int diff = -1;
	vector<unsigned int> v(N);
	for (int i = 0; i < N;i++) {
		unsigned int temp; cin >> temp;
		v[i] = temp;
	}
	sort(v.begin(), v.end());
	for (int i = 1; i < N;i++) {
		if (v[i] - v[i - 1] == 0) { cout << "NO" << endl; return 0; }
		if (diff == -1) { diff = v[i] - v[i - 1]; }
		else {
			if (diff != v[i] - v[i - 1]) {
				cout << "NO" << endl; return 0;
			}
		}
	}
	cout << "YES" << endl;
	return 0;
}