Math Riddle

Three men go to rent a room for the night. The hotel clerk said it's $30. They each give him $10. On the way up, the clerk realized he over-charged them. Instead of $30, it's $25. He gives the bellboy $5 and said to give it to the 3 men. On the way up, the bellboy gets greedy. He thinks, "Why should I give them all $5? I'll give them each $1 and keep $2 for myself". So he gave them each $1 back. So instead of paying $10 each, they each spent only $9. Now, $9 X 3 men = $27. Plus the $2 that the bellboy kept, equals $29. What happened to the other $1?