instruction: what is the number of patients whose diagnoses long title is ulcer of heel and midfoot and drug route is dwell?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id WHERE diagnoses.long_title = "Ulcer of heel and midfoot" AND prescriptions.route = "DWELL"