用函数求斐波那契数列的前n项的和。n要求从系统参数得到。

import sys

def fibonacci_sum(n):
    if n <= 0:
        return 0
    elif n == 1:
        return 1
    else:
        sum = 1
        prev = 0
        current = 1
        for i in range(2, n+1):
            next = current + prev
            sum += next
            prev = current
            current = next
        return sum

if __name__ == '__main__':
    n = int(sys.argv[1])
    result = fibonacci_sum(n)
    print(result)