The first stage ends when they drop the four boosters. If you mean when they drop the core too, then that's the end of the second stage. Either way, I'm not sure, probably something like 2-2.5km/s at booster jettison and 5-6km/s at core jettison. From playing enough KSP, I know that the dV needed to reach ISS is around 10km/s dV. But the actual speed at that orbit is around 8km/s due to atmospheric losses. So the last stage does the rest of the ~2km/s to bring it up to the ISS. Then the capsule itself does small adjustments to line it up for docking with negligible dV budget. But don't take my word for it, these are ballpark numbers I'm throwing around from what I've seen before.

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