SSRS Percentage matrix in a row

Hi guys, having a simple report like this:

COMP   2012   2013   tot

A           100   200     300 

B             50   100     150

tot         150   300     450

I'd like to add a percentage per year. I mean

COMP   2012  %  2013  %   tot  %

A           100   66   200 66    300  66 

B             50   33   100 33    150  33

tot         150   100 300 100   450 100

I tried with: =Sum(Fields!Price.Value)/Sum(Fields!Price.Value, "DataSet1")

but it returns the percentage of all total, not splitted year by year. Any idea?

Thanks