I woke up, and realized I am inside a room.
The room has two doors.
Both doors have a guard in front of it.
On the wall, there is a message:
"One of the guard always tells the truth, while the other always tells lies.
One of the doors is the door to heaven, while the other is the door to hell.
You are only allowed to choose one of the guards and ask only one question."
What question should I ask in order to know which door is the door to heaven? And ask who?