x,a[1<<17],s;c(int*a,int*b){x=*a-*b;}main(i){for(;~scanf("%d",a-i);i--);for(qsort(a,-i,4,c);++i&&(s==(x=a[-i]-a[~i])|!s?s=x:0););x=!puts(i?"NO":"YES");}