Dosun-Fuwari

Dosun-Fuwari is a Japanese logic puzzle. You need to place iron balls and balloons in the grid so that both are immovable.

Rules: Place exactly one black circle and one white circle in each region.
Black circles are iron balls; they must rest on the bottom edge of the diagram, on a black square or another iron ball.
White circles are balloons; they must rest on the top edge of the grid, on a black square or another balloon.