#include <stdio.h>
#include <stdlib.h>

int cmp(const void* n1, const void* n2)
{
	if (*(int*)n1 > *(int*)n2) {
		return 1;
	}
	else if (*(int*)n1 < *(int*)n2) {
		return -1;
	}

	return 0;
}


int main()
{
	int N, flag = 1, distance = -1;
	int* x;

	if (scanf("%d", &N) != 1) {
		return -1;
	}

	x = (int*)malloc(sizeof(int) * N);

	if (x == NULL) {
		return -1;
	}

	for (int i = 0; i < N; i++) {
		if (scanf("%d", &*(x + i)) != 1) {
			return -1;
		}
	}

	qsort(x, N, sizeof(int), cmp);

	for (int i = 0; i < N - 1; i++) {
		if (*(x + i) == *(x + i + 1)) {
			flag = 0;
			break;
		}

		if (distance == -1) {
			distance = *(x + i + 1) - *(x + i);
		}

		if (*(x + i + 1) - *(x + i) != distance) {
			flag = 0;
			break;
		}
	}

	if (flag == 1) {
		printf("YES");
	}
	else {
		printf("NO");
	}

	free(x);
	x = NULL;

	return 0;
}