The ornamental design for a walkingstick, as shown and described.
FIG. 1 is a front view of the walking stick embodying my new design.
FIG. 2 is a close up view of the top portion of FIG. 1.
FIG. 3 is a rear view of FIG. 2.
FIG. 4 is a right side view of FIG. 2, the left side view being a mirror image thereof; and,
FIG. 5 is a top view of the walking stick.
The broken lines showing a portrayal of the figure disposed on the top of the walking stick and the figure in the oval medallion are included for the purpose of illustrating portions of the walking stick and form no part of the claimed design.