A 27-year-old man presents to clinic for assessment of new left-sided chest pain and feeling unwell. He describes developing a new cough with some blood-tinged sputum, fever, and chills of 2 days duration. His past medical history is negative, and he reports smoking about 1 pack a day. On physical examination, the pertinent findings are dullness and crackles in the left lower chest. His CXR is shown in Figure below. Which of the following is the most likely diagnosis?