How many races take place in Dessau circuit?
{'header': ['Race Name', 'Circuit', 'Date', 'Winning driver', 'Constructor', 'Report'], 'page_title': '1952 Formula One season', 'section_title': 'East German Championship', 'caption': 'East German Championship', 'rows': [['I Rostock Osthafenkurs', 'Rostock', '20 April', 'Paul Greifzu', 'BMW - Eigenbau', 'Report'], ['I Bernau Autobahnschleife', 'Bernau', '4 May', 'Rudolf Krause', 'BMW - Reif', 'Report'], ['I Dessau Autobahnspinne', 'Dessau', '11 May', 'Fritz Riess', 'Veritas-Meteor', 'Report'], ['III Leipzig Stadtparkrennen', 'Leipzig', '2 June', 'Edgar Barth', 'IFA - Kollektiv', 'Report'], ['III Strassen-Rennen Halle-Saale-Schleife', 'Halle-Saale-Schleife', '8 June', 'Edgar Barth', 'IFA - Kollektiv', 'Report'], ['I Strassen-rennen Leipzig', 'Leipzig', '17 August', 'Hans Stuck', 'AFM - BMW', 'Report'], ['V DMV Grenzlandringrennen', 'Grenzlandring', '31 August', 'Toni Ulmen', 'Veritas', 'Report']]}