panic: invalid argument to Intn

goroutine 1 [running]:
math/rand.(*Rand).Intn(0x4?, 0x40000c7b80?)
	/usr/local/go/src/math/rand/rand.go:180 +0x64
main.generateCase(0x40000c7e68)
	/home/ubuntu/codeforces/0-999/400-499/430-439/437/verifierD.go:99 +0x58
main.main()
	/home/ubuntu/codeforces/0-999/400-499/430-439/437/verifierD.go:177 +0x1d8
exit status 2