input: Write a function to calculate the Fibonacci number up to a given number n. If n is 0, return 0. If n is 1, return 1. For any other number n, return the sum of the Fibonacci number for n-1 and n-2.
  assert Fibonacci(5)==5
  assert Fibonacci(10)==55
  assert Fibonacci(0)==0
  assert Fibonacci(1)==1
  assert Fibonacci(7)==13
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