input: Write a function to calculate the square of the incremented value of a given number using two helper functions.
  assert f2(2) == 9
  assert f2(3) == 16
  assert f2(0) == 1
output: def increment(x):
      return x + 1
  
  def square(x):
      return x * x
  
  def f2(x):
      return square(increment(x))