FIG. 1 is a perspective view of a desk showing our new design; FIG. 2 is a front view of thereof; FIG. 3 is a rear view thereof; FIG. 4 is a left side view of thereof; FIG. 5 is a right side view thereof; FIG. 6 is a top view thereof; and, FIG. 7 is a bottom view thereof. The broken lines are for environmental purposes only and form no part of the claimed design.