Challenge: fastest program wins

Write a program in your language that
1.opens a file as arbitrary precision integer.
2.divides the number by 3.
3.stores the binary result in another file.

What sort of fucking idiot regards "opens a file as arbitrary precision integer" to mean "read in a file, interpret it as ASCII and take that string to be a base 10 number"? Obviously, it means take the actual file data to be a number.