ผู้ป่วยที่เป็นโรคต้นกำเนิดและปีที่เข้ารับการรักษาน้อยกว่า 2,155 ปีมีจำนวนเท่าใด ไม่จำเป็นต้องใช้ตารางทั้งหมด
what is the number of patients whose primary disease is stemi and admission year is less than 2155?It is not neccessary to use all the tables.
 demographic:  subject_id [ text]  hadm_id [ text]  name [ text]  marital_status [ text]  age [ text]  dob [ text]  gender [ text]  language [ text]  religion [ text]  admission_type [ text]  days_stay [ text]  insurance [ text]  ethnicity [ text]  expire_flag [ text]  admission_location [ text]  discharge_location [ text]  diagnosis [ text]  dod [ text]  dob_year [ text]  dod_year [ text]  admittime [ text]  dischtime [ text]  admityear [ text] 
SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic WHERE demographic.diagnosis = "STEMI" AND demographic.admityear < "2155"