Author: Vladimir Portugalov
Shade some cells so that every outlined region contains exactly 2 shaded cells. Every shaded cell should share an edge with exactly one other shaded cell.
Grid control: Click the mouse button at the selected cell to change the color of the cell. Second click will put auxiliary cross sign, which doesn't affect correctness of the solution, but helps visually. You can also drag the content of one cell to another with the mouse. More details about grid control are at the help page.