#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <utility>
#include <iomanip>
using namespace std;
#define diff(x, y) ((x) > (y) ? ((x) - (y)) : ((y) - (x)))

int main(void) {
	int n, sa;
	bool ans = true;
	cin >> n;
	vector <long int> x(n);
	for (int i = 0; i < n; i++)
		cin >> x[i];
	sort(x.begin(), x.end());
	sa = x[1] - x[0];
	for (int i = 1; i < n; i++) {
		if (x[i] - x[i - 1] != sa || x[i] == x[i - 1]) ans = false;
	}
	if (ans)	cout << "YES" << endl;
	else		cout << "NO" << endl;
	return 0;
}