MultiSelect DropDown

Hi all

i fight with a problem

I have a MultiSelect Drpown Down with some entries like

CH - Switzerland

RO1 - Romania

DE - Germany

US1 - Fremont

and and and

I want now in a "Calculated Column" just the Stuff before the - in one one 

as an example, f somebody select RO1 and CH I want in the other Column RO1CH

how can I do this, I think this thing will make me crazy