#include <stdio.h>
#include <stdlib.h>
int comp(const void *a, const void *b)
{
return (*(int *)a - *(int *)b);
}
int main()
{
	int N;
	int *x;
	int i;
	int diff;

	scanf("%d\n", &N);
	x = (int *)malloc(sizeof(int)*N);
	for (i = 0; i < N; i++) {
		scanf("%d", &x[i]);
	}

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

	for (i = 0; i < N - 1; i++) {
		if (x[i] == x[i + 1]) {
			printf("NO\n");
			return 0;
		}
	}

	diff = x[1] - x[0];

	for (i = 0; i < N - 1; i++) {
		if (diff != x[i + 1] - x[i]) {
			printf("NO\n");
			return 0;
		}
	}

	printf("YES\n");
	return 0;
}