A city bus travels its usual route. At the first stop, 1 person boards; the total number of passengers is now divisible by 5. At the second stop, 2 people get off; the total number of passengers is now divisible by 2. At the third stop, 6 people board; the total number of passengers is now divisible by 4. If the bus holds at most 25 riders, how many passengers were on the bus before the first stop?
