when for the first time until 02/2104 was patient 13806 prescribed insulin and potassium chloride (powder) at the same time?
select t1.startdate from ( select admissions.subject_id, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where prescriptions.drug = 'insulin' and admissions.subject_id = 13806 and strftime('%y-%m',prescriptions.startdate) <= '2104-02' ) as t1 join ( select admissions.subject_id, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where prescriptions.drug = 'potassium chloride (powder)' and admissions.subject_id = 13806 and strftime('%y-%m',prescriptions.startdate) <= '2104-02' ) as t2 on t1.subject_id = t2.subject_id where datetime(t1.startdate) = datetime(t2.startdate) order by t1.startdate asc limit 1