input: Write a function to debug the given Python code and ensure it runs correctly. The function should define two functions f1 and f2, where f1 increments the input by 1 and f2 returns the square of the result of f1 applied to the input. Finally, the function should call and print the result of f2 with the input 2.
  
  def f1(x):
      return x + 1
  
  def f2(x):
      return f1(x) * f1(x)
  
  print(f2(2)) #Output: 9
  
  assert f2(2) == 9
  assert f2(0) == 1
  assert f2(-1) == 0
  assert f2(3) == 16
  assert f2(-3) == 4
output: def f1(x):
      return x + 1
  
  def f2(x):
      return f1(x) * f1(x)
  
  print(f2(2))