Period.

This boy, he's in kindergarten, and his teacher gives them an assignment: Go home, figure out what letter of the alphabet you think is needed the most.  Come back and tell us about it and why.

Well he goes home, and when he gets back the teacher gets to him, he walks up to the board, puts a "." on it, and sits back down.

"Is.. that a period?"

"Yes, does it count as a letter?"

"I suppose so.. but why do you think it's so important?"

"Well.. this morning my sis said she was missing one, and when she said it my Mom passed out, my Dad had a heartattack, and the guy next door shot himself."