The ornamental design for a fan, as shown and described.
FIG. 1 is a bottom perspective view of our design for a fan;
FIG. 2 is a top perspective view of the fan;
FIG. 3 is a front view of the fan, the rear view being a mirror image thereof;
FIG. 4 is a left side view of the fan, the right side view being a mirror image thereof;
FIG. 5 is a top view of the fan;
FIG. 6 is a bottom view of the fan; and,
FIG. 7 is an enlarged partial view of the area indicated in FIG. 6.
The dash-dash broken line depictions of portions of the fan form no part of the claimed design. The dot-dash broken lines encircling portions of the fan in FIG. 6 and FIG. 7 form no part of the claimed design.