A 45-year-old female patient complains of fever, appearance of rash in the mouth cavity and on the lips. She has a 4-year history of this disease which occurs mainly in autumn and spring. Objectively: oral mucosa is hyperemic, there are painful erosions covered with gray plaque. There are also hemorrhagic crusts on the lips. The skin of the forearm flexor surfaces exhibits maculo-papular rash. What is the most likely diagnosis?