Which book has the most written characters in the world?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'INTERNAL', 'name_': 'Q6173448', 'id': 0, 'label': 'Wikipedia:Vital articles/Level/4'}, {'type': 'INTERNAL', 'name_': 'Q5', 'id': 1, 'label': 'human'}, {'type': 'INTERNAL', 'name_': 'Q577', 'id': 2, 'label': 'year'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q571', 'id': 3, 'label': 'book'}, {'type': 'INTERNAL', 'name_': 'Q9135', 'id': 4, 'label': 'operating system'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q95074', 'id': 5, 'label': 'fictional character'}], 'links': [{'name_': 'P5008', 'source': 1, 'target': 0, 'label': 'on focus list of Wikimedia project'}, {'name_': 'P1889', 'source': 1, 'target': 5, 'label': 'different from'}, {'name_': 'P5008', 'source': 2, 'target': 0, 'label': 'on focus list of Wikimedia project'}, {'name_': 'P5008', 'source': 4, 'target': 0, 'label': 'on focus list of Wikimedia project'}, {'name_': 'P1963', 'source': 4, 'target': 2, 'label': 'properties for this type'}, {'name_': 'P1963', 'source': 4, 'target': 3, 'label': 'properties for this type'}]}