Giant, Slimy, Boy, Romy and Fatty want to cross a river. To cross the river there is a small boat. The boat only has 4 spaces. Every one can row the boat.
At the boat, Giant needs 4 spaces. Slimy only needs 1 space, Boy also only needs 1 space. Romy needs 2 spaces, and Fatty needs 3 spaces.
Slimy and Romy will fight to death if they left alone. Slimy and Fatty also can not left alone. Boy and Fatty can not left alone too. ("can not left alone" means both "at" and "out of" the boat).
How do they cross the river, with only 7 trips.