Help King Thorin in his quest

Smaug, the dragon, rules under The Mountain, Erabor which was originally the ruling place of Dwarf King. King Thorin, who is the rightful heir to the throne is on his way to take back his kingdom from Smaug. With the help of a map, King Thorin is able to find a secret entry into the mountain. But now when he has reached the door, he finds that the door has been sealed and can only be unlocked usin