Password Problem

A man wanted to enter an exclusive club but did not know the
password that was re quired. He waited by the door and
listened.A club member knocked on the door and the
doorman said, "twelve." The member replied, "six " and was
let in.A second member came to the door and the doorman said,
"six." The member replied, "three" and was let in.The man
thought he had heard enough and walked up to the door.
The doorman said ,"ten" and the man replied, "five.
"But he was not let in. What should have he said?