input: Write a function to debug the given Python code provided below. The function should correctly define f1 and f2, and return the correct output when calling f2 with the input value.
  def f1(x):
      return x + 1
  
  def f2(x):
      return f1(x) * f1(x)
  
  print(f2(2))
  assert f2(2)==9
  assert f2(3)==16
  assert f2(-1)==0
  assert f2(0)==1
output: def f1(x):
      return x + 2
  
  def f2(x):
      return f1(x) * f1(x)