1:  3(13,11,2) 2(16,12,4)
2:  1(0,0,12) 4(12,12,0) 3(10,0,10)
3:  4(0,0,0) 1(0,0,11) 5(14,11,3) 2(4,0,4)
4:  5(0,0,7) 2(0,0,12) 6(20,19,1) 3(9,0,9)
5:  3(0,0,11) 6(4,4,0) 4(7,7,0)
6:  5(0,0,4) 4(0,0,19)
total flow = 23