80.

David killed two thirds of the Moabite POWs and enslaved the rest

How should we treat prisoners of war? Fortunately, as with so many difficult questions, the Bible has the answer!

Bible believers don't need to worry about the Geneva Convention. God tells them directly what to do with their POWs in the Bible. All they have to do is follow David's example.

David ... smote Moab, and measured them with a line, casting them down to the ground; even with two lines measured he to put to death, and with one full line to keep alive. And so the Moabites became David's servants, and brought gifts. 2 Samuel 8:1-2

So when it comes to POWs, we know what is right in the eyes of the Lord: kill two-thirds of them and enslave the rest.

That is the Bible's infallible answer.

(My estimate of 667 is two thirds of the standard Biblical slaughter of 1000.)