A 55-year-old patient complains of general weakness, spasmodic neuralgic pain in the right side of face, rash in the mouth and on the skin. Objectively: lip and chin skin is markedly hyperemic, there are numerous vesicles with clear exudate on the right. The right cheek mucosa is hyperemic, there is a string of erosions covered with fibrinous pellicle. What is the provisional diagnosis?