The problem of people crossing the river with ghosts

Two ghosts go first. Come back by accident. There is a ghost across the street. There are three people and two ghosts here.

Two ghosts in the past. Come back by accident. There are two ghosts across the street. There are three people and a ghost here.

Two people in the past. One ghost at a time. Across the street, one person and one ghost. There are two people and two ghosts here.

The last two have passed. A ghost is back. There are three people across the street. There are three ghosts here.

There are only three ghosts left, two in the past, one coming back to pick up the other.

This is it ~