Slitherlink

Slitherlink (Fences, Great Wall of China, Loop the Loop, Loopy, Number Line, Dotty Dilemma, Sli-Lin, Takegaki) is a logic puzzle. Draw a loop on the grid lines.

Rules: A single loop must be drawn in the grid along the grid lines, which does not pass through any grid point more than once, but does not necessarily pass through all grid points.
A number in a cell indicates how many grid lines around the cell are used by the loop. Any number of lines can be drawn around a cell without a number.