instruction: tell me the length of stay of patient 012-18025's first stay at the icu.
response: SELECT STRFTIME('%j', patient.unitdischargetime) - STRFTIME('%j', patient.unitadmittime) FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '012-18025') AND NOT patient.unitadmittime IS NULL ORDER BY patient.unitadmittime LIMIT 1