def fibonacci(k): if k <= 0: return "输入错误，k应为正整数。" elif k == 1 or k == 2: return 1 else: a, b = 1, 1 for _ in range(3, k + 1): a, b = b, a + b return b # 假设输入的k为19 k = 19 print(fibonacci(k))