input: Write a function to debug the given Python code by correcting the issues and returning the correct output. If the correction is done correctly, the output should be 9 when f2(2) is called.
  
  def f1 (x):
   return x + 1
  def f2(x):
   return f1(x)*f1(x)
  
  assert f2(2)==9
  assert f1(2)==3
  assert f2(0)==1
  
  # Output:
  # define f1 #
  def f1(x):
      return x + 1
  
  # define f2 #
  def f2(x):
      return f1(x) * f1(x)
  
  # call f2 #
  print(f2(2)) #Output: 9
output: def f2(x):
      return f1(x) * f1(x)