The ruling on one who enters the prayer alone, then another congregation is established

I entered the mosque and the imam had already finished the prayer, so I began the prayer. Then two people entered behind me to join a second congregation. What is the ruling regarding me?
If he completes his prayer, there is no blame on him. And if he leaves it and starts the prayer anew with the two who entered, there is no blame, because the reward for the first prayer has ended.Meaning: The second congregation does not attain twenty degrees, but there is no doubt that a man’s prayer with another man is better than the prayer of one alone.