Subtract from number the sum of its digitsΒΆ

Write a python program that accept a positive number
and subtract from this number the sum of its digits and so on.
Continues this operation until the number is positive.
def repeat_times(n):
    s = 0
    n_str = str(n)
    while (n > 0):
        n -= sum([int(i) for i in list(n_str)])
        n_str = list(str(n))
        s += 1
    return s

print(repeat_times(9))
print(repeat_times(21))

Output:

1
3