[[1,2],   [2,10],  [10,11], [11,8],  [8,1],
 [1,5],   [2,3],   [9,10],  [20,11], [7,8],
 [5,4],   [4,3],   [3,12],  [12,9],  [9,19],
 [19,20], [20,17], [17,7],  [7,6],   [6,5],
 [4,14],  [12,13], [18,19], [16,17], [15,6],
 [14,13], [13,18],[18,16],  [16,15], [15,14]]