I claim the ornamental design for an induction cooktop, as shown and described.
FIG. 1 is a perspective view of an induction cooktop, showing my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a left side elevational view thereof; and,
FIG. 5 is a front elevational view thereof.
Broken lines are for illustrating unclaimed portions of the induction cooktop; the broken lines form no part of the claimed design. A right side elevation view is identical to the left side elevational view as shown in FIG. 4, and a rear elevational view is identical to the front elevational view as shown in FIG. 5.