Author: Andrey Bogdanov
Draw a single, non-intersecting loop that only consists of horizontal and vertical segments. Numbers inside a cell indicate the number of quadrants of that cell that are inside the loop.
Grid control: To draw a line press the mouse button at a start cell and move mouse to another cell holding the button. You can also put auxiliary marks which don't affect submission by clicking at grid nodes. More details about grid control are at the help page.