instruction: how many of the patients with personal history of malignant neoplasm of other gastrointestinal tract had a hospital stay of more than 15 days?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id WHERE demographic.days_stay > "15" AND diagnoses.long_title = "Personal history of malignant neoplasm of other gastrointestinal tract"