A 54-year-old man developed a pustule on the skin of his chin. The pustule rapidly progressed into a hard and sharply painful infiltration 3x3.5 cm in size. The skin over the infiltration is bluish-red. In its center there are three necrotic foci surrounding the hair follicles. Palpation detects enlarged and painful submental lymph nodes. The body temperature is 38.5°C. Make the provisional diagnosis: