input: Write a function to debug the given Python code by ensuring that the function `f1` returns a value and that both functions `f1` and `f2` are defined correctly. Return the result of calling `f2(2)`.
  assert f2(2) == 9
  assert f2(0) == 1
  assert f2(-1) == 0
  assert f2(3) == 16
  assert f2(-2) == 1
output: def f1(x):
      return x**2
  
  def f2(x):
      return f1(x) + 1