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

int sortfnc(const void *a,const void *b){
	if(*(int*)a == *(int*)b){return 0;}
	if(*(int*)a < *(int*)b){return -1;}
	return 1;
}

int main(void){
	int n,w[131072],i,t = 0;
	scanf("%d",&n);
	for(i = 0;i < n;i++){scanf("%d",&w[i]);}
	qsort(w,n,sizeof(int),sortfnc);
	if(w[1]-w[0] != 0){t = w[1] - w[0];}else{printf("NO\n");return 0;}
	for(i = 1;i < n-1;i++){if(t != w[i+1] - w[i]){printf("NO\n");return 0;}}
	printf("YES\n");
	return 0;
}