A 26-year-old has acute onset of non-productive cough and right sided pleuritic chest pain for 2 days. He is an IV drug user, with his last use approximately 4 days ago. On exam, Temp 39.4C, BP= 120/80mmhg, pulse rate 100/min, RR 20/min. Cardiopulmonary exam reveal clear lungs and grade 3/6 holosystolic murmur heard best at the lower sternal border that increase on inspiration. Chest radiograph reveals small infiltrate in left upper lobe, Rt upper lobe, and Rt lower lobe. Blood culture obtained. Most likely diagnosis?