A 68-year-old patient has been taking diclofenac because of pain in the knee joints for about a year. In the evening after substantial meal the patient presented with liquid black stool, drastic weakness, single vomiting after which the patient lost consciousness. Emergency team delivered him to the hospital. Objectively: the patient is conscious, with slightly deferred reaction, pale. Heart rate is 20 breaths/min, Ps is 102 bpm, AP is 110/70 mm Hg. Abdomen is soft, painful in the epigastrium. What is the most likely di- agnosis?