instruction: calculate the length of stay of the last stay of patient 005-46456 in 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 = '005-46456') AND NOT patient.unitadmittime IS NULL ORDER BY patient.unitadmittime DESC LIMIT 1