when was the first time patient 13806 had had an intake on 01/21/2102?
select inputevents_cv.charttime from inputevents_cv where inputevents_cv.icustay_id in ( select icustays.icustay_id from icustays where icustays.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 13806 ) ) and strftime('%y-%m-%d',inputevents_cv.charttime) = '2102-01-21' order by inputevents_cv.charttime asc limit 1