How does a resident who caught one rak'ah with a congregation shortening the prayer complete his 'Isha prayer?

A resident is required to complete the prayer, even if he prays behind someone who is shortening it. The latecomer must stand up after the Imam's salutation, recite Al-Fatiha and another surah, then sit for the tashahhud, then perform two more rak'ahs in which he recites only Al-Fatiha, then sit for the final tashahhud and say the taslim.