s1 -> s2
s2 -> s3
s3 -> s4
s4 -> s1
s2 -> s4
s1 -> s5
s5 -> s1
s1 -> s6
s6 -> s1
s1 -> s7
s1 -> s9
s1 -> s8
s9 -> s10
s8 -> s10
s1 -> s11
s11 -> s1
s1 -> s12
s12 -> s1
s1 -> s13
s13 -> s1
s1 -> s14
s14 -> s1
s1 -> s15
s1 -> s16
s16 -> s1
s1 -> s17
s17 -> s1
s7 -> s1
s15 -> s10