vlookup and sumif - based on cell content

in e6 filled down
=IF(COUNTIF($C$6:C6,C6)=1,SUMIF($C$6:$C$100,C6,$D$6:$D$100),"")

Thanks a lot - one more question - is there any chance that the other rows stay blank?
see attached file - now it is summing it in the first row and the others are showing the individual value..
also .. in case the document is large and the portfolio numbers go down to 100s, is this formula still the best one?

thanks a lot

using it in a another file it does not work - is there possibly another way? or not?
thanks

you havent entered the formula correctly notice the $ signs you need then to anchor the cell reference
=IF(COUNTIF($C$6:C6,C6)=1,SUMIF($C$6:$C$100,C6,$D$6:$D$100),"")