#Butterfly network with 8 terminal nodes and 12 switches
20 4

 0 T  8
 1 R  8
 2 R  9
 3 R  9
 4 R 10
 5 R 10
 6 R 11
 7 R 11
 8 N 12 14
 9 N 13 15
10 N 12 14
11 N 13 15
12 N 16 17
13 N 16 17
14 N 18 19
15 N 18 19
16 N  0  1
17 N  2  3
18 N  4  5
19 N  6  7