input: Write a python function to calculate the number of k-sized cubes that can fit inside an n-sized cube.
  assert No_of_cubes(2,1) == 8
  assert No_of_cubes(5,2) == 64
  assert No_of_cubes(1,1) == 1
output: def No_of_cubes(n, k):
      return (n // k) ** 3