python 1109: 数根（函数专题）

def digitsum(m):
    a=[]
    c=0
    for i in str(m):
        a.append(i)
    for j in a:
        c+=int(j)
    return c
a=int(input())
while digitsum(a)//10!=0:
    a=digitsum(a)

print(digitsum(a))