We claim the ornamental design for a fan, as shown and described.
FIG. 1 is a perspective view of the fan showing our new design;
FIG. 2 is a front view of the fan shown in FIG. 1;
FIG. 3 is a rear view of the fan shown in FIG. 1;
FIG. 4 is a right view of the fan shown in FIG. 1;
FIG. 5 is a left view of the fan shown in FIG. 1;
FIG. 6 is a top view of the fan shown in FIG. 1; and,
FIG. 7 is a bottom view of the fan shown in FIG. 1.
The broken line showing of the top hanging hook and attachment means is included for the purpose of illustrating environmental structure and forms no part of the claimed design.