The history of a 70-year-old patient states that the disease onset was approximately six months ago. According to her relatives, her memory of current events was sharply deteriorating, in particular, she was forgetting the way home when returning from the store and started experiencing difficulties while performing her usual daily activities. The memory of past events was retained. Signs of semantic and amnestic aphasia were observed. Echolalia is periodically noted. The patient is in a low mood and has slight anxiety. She has a history of craniocerebral trauma and had diabetes mellitus for approximately 15 years. What is the most likely diagnosis in this case?