I read a joke before and forgot it. Everybody help me find it.

One day, the mental hospital began to choose the building director of the patient. On the third floor, the dean came to the men's ward on the first floor with an apple in his hand and asked what it was. Someone answered Apple, and the dean said it was absolutely right. You are the director on the first floor. Then I went to the female hospital bed on the second floor, took a bunch of grapes and asked what it was. Someone answered grapes, and the dean said it was absolutely right. You are the director on the second floor. Finally, the dean came to the critically ill bed on the third floor. A patient has the yellow skin of a shellfish in his hand. He needs to eat something. Then he asked the dean. What's in my hand? The dean said banana, and then the patient said it was absolutely right. You are the director on the third floor.