Passage: He was born in Rome, the son of a subdeacon. He served as a priest for 40 years before his election and was the first priest to be elected pope since John II in 533. Adeodatus represents the second wave of anti-Gregorian challenge to the papacy, the first being that of Sabinian.  He reversed the practice of his predecessor Boniface IV of filling the papal administrative ranks with monks by recalling the clergy to such positions and by ordaining some 14 priests, the first ordinations in Rome since Pope Gregory.According to tradition, he was the first pope to use lead seals (bullae) on papal documents, which in time came to be called "papal bulls". One bulla dating from his reign is still preserved, the obverse of which represents the Good Shepherd in the midst of His sheep, with the letters Alpha and Omega underneath, while the reverse bears the inscription: Deusdedit Papæ.In August 618, an earthquake struck Rome, and later an outbreak of leprosy, during which Adeodatus led the effort to care for the poor and sick. He died 8 November 618. There was a vacancy of one year, one month, and 16 days before his successor was consecrated.His feast occurs 8 November. He is also a saint in the Orthodox Church as one of the pre-Schism "Orthodox Popes of Rome".

Question: How long did Adeodatus serve as a priest before he became Pope?
40 years