start
   def s(a, b, s, e) {
      start
         if (s < e) {
            start
               a := a + b;
               s := s + 1;
               forward a;
               turn 5;
               call s(a, b, s, e);
            end
         }
      end
   }
   down;
   call s(2, 1/100, 0, 1200);
end