
Beginning Zeros

You have a string that consist only of digits. You need to find how many zero digits ("0") are at the beginning of the given string.
Input: A string (str), that consists of digits.
Output: An integer (int).
Examples:
assert beginning_zeros("100") == 0 assert beginning_zeros("001") == 2 assert beginning_zeros("100100") == 0 assert beginning_zeros("001001") == 2
Precondition: 0-9