A 25-year-old female patient complains of marked weakness, sleepiness, blackouts, dizziness, taste disorder. The patient has a history of menorrhagia. Objectively: the patient has marked weakness, pale skin, cracks in the corners of mouth, peeling nails, systolic apical murmur. Blood test results: RBC -3,4 × 1012/l, Hb- 70 g/l, color index - 0,75, platelets -140 × 109/l, WBC- 6,2 × 109/l. What is the most likely diagnosis?