A young woman complained about having vesicles in oral cavity, painful ulcers, especially during talking and eating; muscle and joint pain, body temperature rise, indisposition, weakness. She fell suddenly ill 2 days ago. Objectively: t o- 38,4°C. Vermilion border is covered with bloody crusts that stick together and impede mouth opening. Mucous membrane of lips, cheeks, mouth floor, tongue, soft palate is hyperemic and edematic; there are single vesicles and large painful erosions covered with fibrinous deposit on it. Regional lymph nodes are enlarged and painful. There is hypersalivation. Nikolsky’s symptom is negative. What is the most probable diagnosis?