Column that returns prior year value

I am trying to calculate organic growth for a region and am not able to do this for a measure because it adds the local currencies of the countries together before multiplying by the FX rates to convert back to USD. Because of this I need to translate all the accounts for each country back to USD using the prior year FX rates and then sum the results, so that currencies aren't mixed. 

i.e. - I need  (Country 1 $'s*  PY FX rate) + (Country 2 $'s *PY FX rate) = Organic Dollars

The measure calculates the following  (Country 1 $'s +Country 2 $'s) *(Country 1 PY FX rate+Country 2 PY FX rate) = Incorrect