input: from typing import List
  
  def Fibonacci(n: int) -> int:
      """Compute the nth Fibonacci number.
      If n is less than 0, return an error. If n is 0 or 1, return n.
      Otherwise, return the sum of the (n-1)th and (n-2)th Fibonacci numbers.
      
      >>> Fibonacci(0)
      0
      >>> Fibonacci(1)
      1
      >>> Fibonacci(5)
      5
      >>> Fibonacci(10)
      55
      """
output:     if n < 0:
          raise ValueError("n must be a non-negative integer")
      elif n == 0:
          return 0
      elif n == 1:
          return 1
      else:
          a, b = 0, 1
          for _ in range(2, n + 1):
              a, b = b, a + b
          return b