A 20-year-old male patient complains of acute pain during eating, bad breath, general weakness. Objectively: interdental papillae and marginal gingiva are covered with dirty gray film, any touch is painful. The body temperature is of 37,5°C. Blood count: RBC- 4, 8 × 1012/l, Hb- 150 g/l, colour index - 0,9, WBC- 10, 5 × 109/l, JG- 2%, BASO- 1%, EOS- 5%, segmented neut. - 8%, stabs - 47%, LYM- 35%, PLT- 250 × 109/l. ESR - 20 mm/hour. What is the most likely diagnosis?