#include <stdio.h>

void quickSort(int*, int, int);

int main(void) {
	int b, i, t, n, a[100000];

	scanf("%d", &n);

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

	quickSort(a, 0, n - 1);

	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;
}

void quickSort(int* data, int left, int right) {
	int l, r, temp, t;

	if (left >= right)
		return;

	temp = data[(left + right) / 2];
	l = left;
	r = right;

	while (-1) {
		while (data[l] < temp)
			l++;
		while (data[r] > temp)
			r--;

		if (l >= r)
			break;

		t = data[l];
		data[l] = data[r];
		data[r] = t;
		l++;
		r--;
	}

	if (left < l - 1)
		quickSort(data, left, l - 1);
	if (right > r + 1)
		quickSort(data, r + 1, right);
}