How do u get 4 gallons of water out of a 3 and 5 gallon jug?

Take the 5 gallon jug full of water and pour 3 gallon into the 3 gallon jug leaving 2 in the 5 jug. Empty out the 3 gallon jug and pour the 2 gallons left in the 5 gallon into the 3 gallon jug. refill the 5 gallon jug all the way and fill up the 3 gallon. Now you have 4 gallons left in the 5 gallon jug.