instruction: find out the number of patients admitted before 2123 who were diagnosed with acute on chronic combined systolic and diastolic heart failure.
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id WHERE demographic.admityear < "2123" AND diagnoses.long_title = "Acute on chronic combined systolic and diastolic heart failure"