#include <stdio.h>

int main(void) {
	int b, i, j, t, n, a[100];

	scanf("%d", &n);

	for (i = 0; i < n; i++)
		scanf("%d", &a[i]);

	for (i = 0; i < n - 1; i++)
		for (j = i + 1; j < n; j++)
			if (a[i] > a[j]) {
				t = a[i];
				a[i] = a[j];
				a[j] = t;
			}

	b = 0;
	t = a[1] - a[0];
	for (i = 0; i < n - 1; i++) {
		if (a[i] == a[i + 1] || a[i + 1] - a[i] != t) {
			b = -1;
			break;
		}
	}

	if (b == 0)
		printf("YES\n");
	else
		printf("NO\n");

	return 0;
}