Amos's oracles begin, "For three transgressions of Damascus, even ..." what number?

Answer: Four

Amos repeats "for three transgressions, even four" against each nation in turn, meaning their sins had overflowed.

“This is what the LORD says: “For three transgressions of Damascus, even four, I will not revoke My judgment, because they threshed Gilead with sledges of iron.”— Amos 1:3 (BSB)