Reply sms:A man wanted to enter a club

Reply sms:A man wanted to enter a club
every member knows the password of club,
the man hide himself beside the wall & tried to listen password,
a member came , watchmen said 'twelve' the member reply' 6 '. Watchman open the door,
another member came , watheman said 'six'. Member replyed 3 . Watchman open the door.
MAN THOUGTH HE HAVE GOT THE PASSWORD, HE WENT TO DOOR , WATCHMAN SAID' EIGHT' MAN REPLYED 4
WATCHMEN DID'NT OPEN THE DOOR
WHAT WAS THE PASSWORD.??
THINK AND REPLY ...
REPLY MUST