A 74-year-old man complains of pain in the left foot and dark color of the 1st toe. He has been sick for 6 days. Objectively: heart rate is 84/min. Body temperature is 37,8°C. The left foot resembles "chicken claw" due to soft tissues decreasing in volume, skin is dark red. The 1st toe is black, small amount of dark substance is being discharged from under the nail. Pulse over the peripheral arteries of extremity is absent. The most likely diagnosis is: