What did Caleb say he'd give to whoever could smite Kirjathsepher?

His daughter Achsah for a wife

And Caleb said, He that smiteth Kirjathsepher, and taketh it, to him will I give Achsah my daughter to wife.

And Othniel the son of Kenaz, Caleb's younger brother, took it: and he gave him Achsah his daughter to wife. Joshua 15:16-17