Once there were three old men.They were rather forgetful.They always forgot what they were doing.
One of them said，"I often forget if I should put something in or take something out of the fridge as soon as I open its door."
The second old man said，"I always wonder if I have just come upstairs or am going downstairs when I am standing at the landing.
Then the third one，John said，"I am even more foigetlul than both of you."The last old man knocked at the table.Then he turned to the other two men，"Who just knocked the table？"
"Mr John."they answered.
"And where is Mr John？"