input: Write a python function to generate the nth Fibonacci number.
  assert Fibonacci(10) == 34
  assert Fibonacci(5) == 3
  assert Fibonacci(0) == 0
  assert Fibonacci(1) == 1
  assert Fibonacci(2) == 1
output: def Fibonacci(n):
      if n == 0:
          return 0
      elif n == 1:
          return 1
      a, b = 0, 1
      for _ in range(2, n + 1):
          a, b = b, a + b
      return b