source	target	weight
1	2	2
1	3	1
4	2	3
4	3	2
4	1	3
5	1	2
6	5	2
7	5	2
6	7	1
8	1	1
8	9	4
9	10	1
8	11	1
12	11	1
12	8	1
13	10	1
13	9	1
