Author: Andrey Bogdanov
Shade some cells black and then draw a single non-intersecting loop through all white cells. Black cells cannot share an edge with each other. Cells that contain clues or shaded grey are not part of the loop. Numbered arrows in such cells indicate the number of cells shaded black in that direction in the grid.
Grid control: To draw a line press the mouse button at a start cell and move mouse to another cell holding the button. Mouse click at a cell paint the cell black. More details about grid control are at the help page.