Top or Bottom Bunk

After separate but lengthy trials two guys meet in a prison-cell and tried to get the upper or lower bunk. PRISONER #1: How long are you here for?  PRISONER#2 : Twenty-seven years. Hwo long are you in for?  PRISIONER #1 : Twenty-five years.  PRISONER #2 : Well,then, you sleep by the door: you'll get out before me.