The ornamental design for the fan, as shown and described.
FIG. 1 is a front perspective view of the fan;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof;
FIG. 8 is a partial enlarged view of the area indicated in FIG. 1 thereof; and,
FIG. 9 is a partial enlarged view of the area indicated in FIG. 2 thereof.
The broken lines depict portions of the fan that form no part of the claimed design; the broken lines encircling portions of the fan in FIGS. 1 and 2 and illustrated in enlarged views in FIGS. 8 and 9 form no part of the claimed design.