Bob the Builder

Bob has taken a contract to complete two walls $w1$ and $w2$. Since, previous builder left the walls incomplete, bob needs the complete the walls. Formally, the two walls will be having height $w1$ and $w2$ before Bob starts the work. The height of a wall increases by one unit with each brick kept on top of this wall. Bob has $k$ number of bricks with him and he needs to spend all of these