A 70 year old woman had hip surgery 2 days back for a hip fracture after a fall. There is no history of any past surgery or medication. Over the past 24 hours, she complaint of abdominal discomfo and distension. O/E- she is afebrile with: BP of 140/80 mmHg HR=110 bpm, RR=16 breaths/min She has a distended tympanic abdomen with absent bowel sounds. There is no rebound tenderness. Her erect abdominal X-ray is shown: The most likely diagnosis in this case is?