How does the worshiper complete his prayer if he enters while the Imam is in the second prostration of the second rak'ah? Does he complete it with the Imam and then repeat all four rak'ahs, or does he pray from the beginning?

If the worshiper catches two rak'ahs in the Imam's prayer, he completes two rak'ahs after the Imam's salutation in the four-rak'ah prayer, and one rak'ah in the three-rak'ah prayer. A rak'ah is not considered to have been caught with the Imam unless its bowing (ruku') is caught.