import re


def parse_number(input_):
    """
    Strip everything but digits and + sign; ensure it begins with a country
    code.

    >>> parse_number('5555551212')
    '+15555551212'
    >>> parse_number('12025551212')
    '+12025551212'
    >>> parse_number('+44')
    '+44'
    """
    clean = ''.join(re.findall(r'[\d+]*', input_))
    if not clean.startswith('+'):
        clean = clean.lstrip('1')
        clean = '+1' + clean
    return clean