#include <stdio.h>
#include <algorithm>
using namespace std;
using ll = long long;

//406
int main() {
	int n, x[100000];
	scanf("%d", &n);
	for (int i = 0; i < n; i++)
		scanf("%d", x + i);
	sort(x, x + n);

	int distance = x[1] - x[0], flag = distance != 0;
	for (int i = 2; i < n; i++)
		flag &= (x[i] - x[i - 1]) == distance;
	printf("%s\n", flag ? "YES" : "NO");
}