input: Write a function to calculate the Fibonacci numbers up to a given number `n`. If `n` is 0, return 0; if `n` is 1, return 1; otherwise, return the sum of the two preceding numbers in the sequence.
  
  assert Fibonacci(6)==8
  assert Fibonacci(0)==0
  assert Fibonacci(1)==1
  assert Fibonacci(7)==13
  assert Fibonacci(2)==1
output: def Fibonacci(n):
      if 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