input: def fibonacci(n: int):
      """Get the n-th number in the Fibonacci sequence.
      >>> fibonacci(10)
      55
      >>> fibonacci(1)
      1
      >>> fibonacci(8)
      21
      """
output:     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