python求前n个阶乘的和

i = int(input("input"))
sum = 0
if i<1:
    exit()
else:
    while i>0:
        b = 2
        c = 1
        while b<=i:
            c=b*c
            b=b+1
        sum += c
        i = i-1
        # print(c)
print(sum)