def _parse_url_work_relation(response):
    """ response is
    {'resource': 'https://imslp.org/wiki/7_Bagatelles,_Op.33_(Beethoven,_Ludwig_van)',
 'relations': [{'source-credit': '',
   'target-credit': '',
   'type-id': '0cc8527e-ea40-40dd-b144-3b7588e759bf',
   'type': 'download for free',
   'end': None,
   'direction': 'forward',
   'ended': False,
   'begin': None,
   'target-type': 'work',
   'work': {'title': '7 Bagatelles, op. 33',
    'attributes': [],
    'languages': [],
    'disambiguation': '',
    'type': None,
    'iswcs': [],
    'type-id': None,
    'id': '94a19e47-2c1d-425b-b4f0-63d62d5bf788',
    'language': None},
   'attribute-values': {},
   'attribute-ids': {},
   'attributes': []}],
 'id': '2d264d6e-5082-46a7-a60a-e2d02ab103e1'}
    """
    relations = response.get('relations', [])
    if relations:
        return relations[0]['work']['id']