Club entry!!

A man wanted to enter an exclusive club but did not know the exact password that was required. 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 heard enough and walked up to the door. The doorman said "Ten" and the man replied "Five". But he was not let in. What he should have told?

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