python程序填空

1,n+1
len(a)//2
len(a)//2

1,n+1
len(a)//2
len(a)//2

def sum(n):
    a = [x for x in range(1,n+1)]
    b = (a[0]+a[-1])*(len(a)//2)
    print(a[0],a[-1],len(a)//2)
    if len(a) % 2 !=0:
        b += a[len(a)//2]
    return b


def main():
    n = int(input("n:"))
    print(sum(n))