This exercise is best solved with Python's % (modulo) operator, which returns the remainder of positive integer division.
It has a method equivalent, operator.mod() in the operator module.
Python also offers additional 'remainder' methods in the math module.
math.fmod() behaves like %, but operates on floats.
math.remainder() implements a "step closest to zero" algorithm for the remainder of division.
While we encourage you to get familiar with these methods, neither of these will exactly match the result of %, and are not recommended for use with this exercise.
The built-in function divmod() will also give a remainder than matches % if used with two positive integers, but returns a tuple that needs to be unpacked.