The ornamental design for a cup, as shown and described.
1. Cup
1.1 : Front
1.2 : Back
1.3 : Top
1.4 : Bottom
1.5 : Left
1.6 : Right
1.7 : Reference perspective view
1.8 : Reference perspective view
Reproduction 1.8 is a reference perspective view that the cup shown in the reproduction 1.7 is placed upside down; the part shown in broken lines in the reproduction 1.8 represents a toothbrush inserted in the hole of the handle; the broken line portions in the reproduction 1.8 do not form part of the claimed design.