input: def Fibonacci(n: int) -> int:
      """Generate the nth Fibonacci number.
      >>> Fibonacci(1)
      0
      >>> Fibonacci(2)
      1
      >>> Fibonacci(10)
      34
      """
      if n == 1:
          return 0
      elif n == 2:
          return 1
      else:
          return Fibonacci(n-1) + Fibonacci(n-2)
output:     if n == 1:
          return 0
      elif n == 2:
          return 1
      else:
          a, b = 0, 1
          for _ in range(3, n + 1):
              a, b = b, a + b
          return b