What will be the missing number?

It was three o'clock in the morning, and the receptionist at a posh hotel was just dozing off, when a little old lady came running towards her, screaming. "Please come quickly," she yelled, "I just saw a naked man outside my window!"

The receptionist immediately rushed up to the old lady's room. "Where is he?" asked the receptionist.

"He's over there," replied the little old lady, pointing to an apartment building opposite the hotel. The receptionist looked over and could see a man with no shirt on, moving around his apartment. "It's probably a man who's getting ready to go to bed," she said reassuringly. "And how do you know he's naked, you can only see him from the waist up?"

"The dresser, honey!" screamed the old lady. "Try standing on the dresser!"