.......                     
  ...  .......  .                  
 ...  ...§...  ..                  
 ... #......##..                   
##.##.##. ....##### ##             
..#.. #v..#..##.. .#.   .          
. .....#...# ..#.#..## ..          
 . .. #...v##.##..#..#..           
.....## ##.#..# ...#..#  #         
.##....#.#.v#   #....# ..#         
# #.#.###..######..##.....         
 .#.#.#..........v.......#         
 #....####..#(.#.##...##..         
 #..#.# #.#..#§#........#          
.##.. . #####..#....##...#         
  # . .  .  ###..#.##  ...         
  . .         #....#    #.         
.....         .#...#               
 #            #.## .               
         ∆