求从0至n(n＞0)内所有偶数之和

求从0至n(n＞0)内所有偶数之和
例如输入10输出30
输入8，输出20

def s(n):
    return sum(range(0, n + 1, 2))


print(s(8))

def a(n):
    # 这个最好
    if n < 2:
        return 0
    if n < 4:
        return 2

    if n % 2 != 0:
        n -= 1

    w = int(n / 2)

    return (2 + n) * w / 2


print(a(6))

n = int(input("输入n值:"))
sum = 0
if n % 2 == 0:
for i in range(0,n+1,2):
sum+=i
print(sum)
elif n % 2 == 1:
for i in range(0,n,2):
sum += i
print(sum)