panic: invalid argument to Intn

goroutine 1 [running]:
math/rand.(*Rand).Intn(0x10d868?, 0x40000a4040?)
	/usr/local/go/src/math/rand/rand.go:180 +0x64
main.genCases()
	/tmp/cf-worker-995429241/verifierK.go:54 +0x25c
main.main()
	/tmp/cf-worker-995429241/verifierK.go:109 +0x128