input: Write a function to take an integer input from the user and print its cube. The function should prompt the user for a number, compute its cube, and then print the result.
  assert cube_number(2)==8
  assert cube_number(3)==27
  assert cube_number(0)==0
  assert cube_number(-1)==-1
  assert cube_number(-4)==-64
output: def cube_number(n):
      return n ** 3