def fibonacci(n):
    if n <= 0:
        return "Input should be a positive integer."
    elif n == 1 or n == 2:
        return 1
    else:
        a, b = 1, 1  # 初始化前两项的值
        for _ in range(n - 2):
            a, b = b, a + b  # 更新 a 和 b 的值
        return b

# 例子
n = 6
print(f"斐波那契数列第{n}项的值是：{fibonacci(n)}")