input: Write a function to debug the given Python code which contains two functions, f1 and f2. The function f1 should return x + 1, and the function f2 should return the square of the result from f1. After debugging, calling f2(2) should print the output 9. 
  
  def f1(x):
      return x + 1
  
  def f2(x):
      return f1(x) * f1(x)
  
  assert f2(2) == 9
  assert f1(1) == 2
output: def f1(x):
      return x + 1
  
  def f2(x):
      return f1(x) ** 2