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

int comp(const void *arg1, const void *arg2) {
	return *(int *)arg1 - *(int *)arg2;
}

int check(int arg[], int n) {
	int i, d = arg[1] - arg[0];
	for (i = 1; i < n; i++) {
		if (arg[i - 1] != arg[i]) {
			if (arg[i] - arg[i - 1] != d) return -1;
		}
		else return -1;
	}
	return 0;
}

int main() {
	int n, x[100000], i;

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

	qsort(x, n, sizeof(int), comp);
	if (check(x, n) == 0) printf("YES\n");
	else printf("NO\n");

	return 0;
}