A 22-year-old man at 18:00 developed persisting dull pain in the epigastrium. Three hours later nausea appeared, he vomited once. By the morning the pain shifted to the right iliac area. Body temperature rose to 38.6°C, developed tachycardia of 110/min. On examination there are muscle rigidity and Bloomberg’s sign (rebound tenderness) in the right iliac area of the anterior abdominal wall. Plain X-ray of the abdomen shows no fluid levels, free air under the diapragm on the right. Make the diagnosis: