input: Write a function to calculate the Fibonacci number at a given position. The function should return the Fibonacci number for the provided position. If the position is 0, it should return 0. If the position is 1, it should return 1. For any other position, it should return the sum of the Fibonacci numbers at the two previous positions.
  
  def fibonacci(n):
      if n == 0:
          return 0
      elif n == 1:
          return 1
      else:
          return fibonacci(n-1) + fibonacci(n-2)
  
  assert fibonacci(0) == 0
  assert fibonacci(1) == 1
  assert fibonacci(10) == 55
  assert fibonacci(5) == 5
  assert fibonacci(7) == 13
output: def fibonacci(n):
      if n == 0:
          return 0
      elif n == 1:
          return 1
      else:
          return fibonacci(n-1) + fibonacci(n-2)