A 47-year-old man complains of weakness and dizziness. Half a year ago he undervent a gastric resection. Blood test: Hb - 80 g/L, erythrocytes - 3.5-10/L, color index - 0.69, ESR - 15 mm/hour, serum iron - 5.4 mcmol/L, erythrocyte hypochromia. What type of anemia is the most likely in this patient?