A frog is at the center of a circular shaped island with radius r. The frog jumps 1/2 meters at first. After the first jump, it turns right or left at exactly 90∘, and it always jumps one half of its previous jump. After a finite number of jumps, what is the least r that yields the frog can never fall into the water?<spanclass=′latex−bold′>(A)</span>35<spanclass=′latex−bold′>(B)</span>513<spanclass=′latex−bold′>(C)</span>619<spanclass=′latex−bold′>(D)</span>21<spanclass=′latex−bold′>(E)</span>43