A 19-year-old male patient complains of intense pain in the left knee joint. Objectively: the left knee joint is enlarged, the overlying skin is hyperemic, the joint is painful on palpation. Blood test results: RBC- 3,8 × 1012/l, Hb-122 g/l, lymphocytes - 7,4 × 109/l, platelets - 183 × 109/l. ESR - 10 mm/h. Duke bleeding time is 4 minutes, Lee-White clotting time - 24 minutes. A-PTT is 89 sec. Rheumatoid factor is negative. What is the most likely diagnosis?