Johnny has some number of rectangular bricks. He can put bricks on top of each other to build a tower. He wishes to build two towers of equal height out of his bricks (each tower must contain at least one brick). He also wants the towers to be as tall as possible. Note that Johnny doesn't have to use all the bricks.
You are given a int bricks, where each element is the height of a single brick. Return the height of the tallest towers of equal height that Johnny can build. If it's impossible to build two towers of equal height, return -1 instead.