Should the latecomer say "Allahu Akbar" when standing to complete the third rak'ah after the Imam has said the tasleem, or is the takbir for standing counted from the prostration?

Whoever catches two rak'ahs of Maghrib prayer with the Imam and misses the first rak'ah, then stands to make up the missed rak'ah after the Imam's salutation, should say the takbir when standing up, because he was in a position where sitting is prescribed.