#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

int main() {
	int N;
	cin >> N;
	vector<int> v;
	for (int i = 0; i < N; i++)
	{
		int x;
		cin >> x;
		v.push_back(x);

	}
	sort(v.begin(), v.end());
	int y = v[1] - v[0];
	if (y == 0)
	{
		cout << "NO" << endl;
		return 0;
	}
	for (int i = 0; i < v.size()-1; i++)
	{
		if (y != (v[i + 1] - v[i])) {
			cout << "NO" << endl;
			return 0;
		}
		
	}
	cout << "YES" << endl;
	return 0;
}