The ornamental design for a cup, as shown and described.
FIG. 1 is a perspective view of a cup showing the new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a perspective exploded view thereof.
The broken lines present in the drawings are included for the purpose of illustrating portions of the article which form no part of the claimed design.