وَيُصَلِّي بِالطَّائِفَةِ الْأُولَى رَكْعَتَيْنِ مِنَ الْمَغْرِبِ، وَبِالثَّانِيَةِ رَكْعَةً
Translation: In Maghrib the imam prays two rakahs with the first group and one with the second.
Maghrib has three obligatory rakahs. The imam prays two with group one and one with group two, a 2 + 1 allocation.
Group one later completes one without recitation. Group two completes two with recitation, following the same lahiq/masbuq principle.