For the last 2 months, a 29-year-old woman has been complaining of chest pain on the left, cough, shortness of breath, and fever of 39.6°C. The left half of her chest lags behind in the act of breathing, her vesicular respiration is weakened, and there is a shortening of the percussion sound on the left. X-ray has shown a round shadow in the lower lobe of the left lung. Make the right diagnosis: