For the calulation you load the full flight plan required fuel for the second leg and the flight planned burn off + outbound/first sector contingency, that will give you total fuel required for a two sector trip carrying trip fuel from initial departure.
Don't let anyone talk you out of loading the outbound/first sector contingency fuel. If, for example, you only achieve FL270 instead of flight planned FL370 on the first leg, you will burn contingency and if you didn't include it you would then find at your first stop that you don't have flightplan fuel for the second sector.