A convex polygon has at least one side with length 1. If all diagonals of the polygon have integer lengths, at most how many sides does the polygon have?<spanclass=′latex−bold′>(A)</span>3<spanclass=′latex−bold′>(B)</span>5<spanclass=′latex−bold′>(C)</span>7<spanclass=′latex−bold′>(D)</span>10<spanclass=′latex−bold′>(E)</span>None of the preceding