ἀντ' εὖ ποιεῖν

From LSJ

μέγα γὰρ τὸ τῆς θαλάσσης κράτοςgreat is the power of the country that controls the sea, control of the sea is a great thing, the dominion of the sea is a great matter, the rule of the sea is a great matter, the rule of the sea is indeed a great matter, control of the sea is a paramount advantage

Source

Greek > English (Woodhouse)

benefit in return, repay with good