Different result in TOPN

[sadath]

Hi
I am getting different result in TOPN, similar expression which i tried in dax.do is shown below

EVALUATE
TOPN(4,SUMMARIZE(('Product'),'Product'[Product Name],"SALES",[Sales Amount]))

EVALUATE
VAR X =TOPN(4,ALLSELECTED ('Product'),[Sales Amount])
RETURN FILTER (SUMMARIZE('Product','Product'[Product Name],"SALES",CALCULATE([Sales Amount],KEEPFILTERS (X))),[SALES]>0)

any one knows how the two formula working ?