A 57-year-old retired man complains of attacks of burning pain and rashes on the skin of his face and oral mucosa on the right. Anamnesis: a course of radiation therapy for treatment of gastric disease, past case of chickenpox. Objectively: along the third branch of the trigeminal nerve the skin of the face presents with isolated erosions covered in Hbrinous coating. There are multiple vesicles on the hyperemic and swollen oral mucosa. Right-sided lymphadenitis is observed. What is the most likely diagnosis?