panic: invalid argument to Intn

goroutine 1 [running]:
math/rand.(*Rand).Intn(0x400012a100?, 0x40000106c8?)
	/usr/local/go/src/math/rand/rand.go:180 +0x64
main.generateCase(0x400006cec0)
	/home/ubuntu/codeforces/1000-1999/1800-1899/1860-1869/1864/verifierB.go:47 +0x38
main.main()
	/home/ubuntu/codeforces/1000-1999/1800-1899/1860-1869/1864/verifierB.go:88 +0x18c
exit status 2