yes it was a hard one lol who would think i of all poeple would give a hard riddle ... anyways heres your answer:
SIX YOU WERE RIGHT
Because if you were to ask the guard that tells the truth he would know that the other one would lie so he would say the door to death,
and if you asked the guard that lies he would know that the other guard would say the right door so he would lie about it and say the door that leads to death so you walk out the oppisite door

enjoy - gren