The Room Swimmer

Nobita wants to learn how to swim well, so he asks Doraemon to take out "Room Swimmer" to help Nobita. However, Nobita is able to practice swimming with great difficulty, but he can't get out because he loses his swimming ring. Shizuka and the others go to rescue Nobita, but they can't save him no matter what. Fortunately, Doraemon arrives, and Nobita is able to escape.