A 48-year-old woman complains of disturbed menstrual cycle: her periods last for 7-9 days and arc excessively profuse throughout the last half-year. She notes occasional hot flashes in her head, insomnia, irritability, and headaches. Her skin is of normal color. Blood pressure — 150/90 mm Hg, pulse — 90/min., rhythmic. The abdomen is soft and painless. Bimanual examination shows no uterine enlargement, the appendages cannot be detected. The vaginal fornices are free. What is the most likely diagnosis?