Your code fails to address this --> There are no fractions of people. At the end of each year, the population count is an integer: 252.8 people round down to 252 persons.

Sorry for delay on answering.

You can think about that if you need to move 1 box to the second, then move 100 to first ([1, 100]). See what your code return, compare with the correct answer counting by yourself.

Carefully read the first example in the description.
If needed, perform your algorithm by hand and compare the results for each step.

There are 500 random tests. You should try to optimize more