With accent marks:
Как ау́кнется, так и откли́кнется.
What goes around comes around.
As you treat others, so they will treat you.
This proverb is hard to translate literally. "Аукнется" comes from the sound "ау" that Russian people use to find each other in a forest. "Аукнется" is only used in this proverb, you don't find this word anywhere else. So a close to literal translation can be as follows: as you say "ау", you will receive the same response back.
Other Russian proverbs
Strike the iron while it's hot.
If you like sledding, you should like to carry the sled.
Without labor, you can not even catch a fish in the pond.
Оne sees the mote in another's eye and ignores the log in his own.
One head is good, but two ones are better.
The demon is not as scary as he is depicted.
Don't bring your set of rules in a foreign monastery
In a quiet whirlpool, demons live.