panic: invalid argument to Intn

goroutine 1 [running]:
math/rand.(*Rand).Intn(0x10d4b8?, 0x4000096080?)
	/usr/local/go/src/math/rand/rand.go:180 +0x64
main.generate()
	/tmp/cf-worker-1790980283/verifierE.go:54 +0x150
main.main()
	/tmp/cf-worker-1790980283/verifierE.go:96 +0x134