A man comes into a restaurant at 6 o'clock in the evening.

"I want to have a coffee please."

The waiter brings him the coffee, the man drinks it and afterwards, he orders another, then another, then another.

Finally, at 7:30, the man has drunk 5 coffees.

Said the waiter to the man, when he took care of his bill, "When I drink so much coffee in the evening, I cannot sleep half of the night."

"No problem," said the man. "I count until three - and then I sleep."

"And that works every time?" asks the waiter surprised.

"No, sometimes I count until half past three."