<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def keep_only_digits(s):
    r'''
    local helper to just keep digits
    '''
    fs = ''
    for c in s:
        if c.isdigit():
            fs += c

    return int(fs)