panic: invalid argument to Intn

goroutine 1 [running]:
math/rand.(*Rand).Intn(0x40000a0b58?, 0x285b0?)
	/usr/local/go/src/math/rand/rand.go:180 +0x64
main.genCase(0x40000a0e70)
	/home/ubuntu/codeforces/1000-1999/1700-1799/1770-1779/1776/verifierF.go:26 +0x48
main.main()
	/home/ubuntu/codeforces/1000-1999/1700-1799/1770-1779/1776/verifierF.go:62 +0x280
exit status 2