Club Password

You want to enter a private club but don't know the password to get in. You wait by the door and listen. A club member knocks on the door and the bouncer says "twelve." The member replies "six" and was let in. Another member comes to the door and the bouncer said "six." The member replies "three" and was let in. You thought you'd heard enough and walk up to the door. The bouncer said "ten" and you reply "five" but were not let in. What should you have said to get inside?