On the 4th day after recovery from a cold a patient was hospitalized with complaints of solitary spittings of mucoid sputum. On the 2nd day there was a single discharge of about 250 ml of purulent blood-streaked sputum. Objectively: the patient's condition is moderately severe. Respiratory rate -28-30/min., Ps- 96/min., BP- 110/70 mm Hg. Respiration over the left lung is vesicular, over the right lung weakened. There are various moist crackles over the lower lobe and amphoric breath sounds near the angle of scapula. What is the most likely diagnosis?