How many companies have Postermobile Limited as a parent company?
{'header': ['COMPANY NAME', 'Holding Companies', 'Subsidiaries', 'Description of activities', 'Parent (holding) company'], 'page_title': '', 'section_title': '', 'caption': '', 'rows': [['APOLLO DOMINION INVESTMENTS LIMITED', '5', '0', 'Investment holding company.', 'BESCOT ENTERPRISES LIMITED'], ['CLEAR CHANNEL ENTERTAINMENT FACILITATION LIMITED', '5', '0', 'Financial intermediation', 'CLEAR CHANNEL ENTERTAINMENT (MUSIC) UK LIMITED'], ['LOUIS BARNETT & SON LIMITED', '5', '0', 'Dormant.', 'CLEAR CHANNEL UK LIMITED'], ['POSTERMOBILE LIMITED', '5', '4', 'Selling of advertising space', 'CLEAR CHANNEL UK LIMITED'], ['BARRETT PETRIE SUTCLIFFE LIMITED', '5', '0', 'Advertising', 'CLEAR CHANNEL UK LIMITED'], ['ROCKBOX LIMITED', '5', '0', 'Product advertising.', 'CLEAR CHANNEL UK LIMITED'], ['TRACEMOTION LIMITED', '5', '1', 'The provision of managemenet services', 'CLEAR CHANNEL UK LIMITED'], ['CLEAR CHANNEL (CENTRAL) LIMITED', '5', '12', 'Score outdoor group', 'CLEAR CHANNEL UK LIMITED'], ['F M MEDIA LIMITED', '5', '0', 'Advertising', 'CLEAR CHANNEL UK LIMITED'], ['TAXI MEDIA HOLDINGS LIMITED', '5', '1', 'Dormant.', 'D CLEAR CHANNEL UK LIMITED'], ['CLEAR CHANNEL (NORTH WEST) LIMITED', '6', '2', 'Engaged as outdoor advertising contractors.', 'CLEAR CHANNEL (CENTRAL) LIMITED'], ['CLEAR CHANNEL (SOUTH WEST) LIMITED', '6', '0', 'Dormant.', 'CLEAR CHANNEL (CENTRAL) LIMITED'], ['GROSVENOR ADVERTISING LIMITED', '6', '0', 'Dormant.', 'CLEAR CHANNEL (CENTRAL) LIMITED'], ['POSTERMOBILE ADVERTISING LIMITED', '6', '0', 'Dormant.', 'POSTERMOBILE LIMITED'], ['KMS ADVERTISING LIMITED', '6', '0', 'Dormant.', 'POSTERMOBILE LIMITED'], ['TAXI MEDIA LIMITED', '6', '0', 'Taxi advertising contractors', 'TAXI MEDIA HOLDINGS LIMITED']]}