panic: invalid argument to Intn

goroutine 1 [running]:
math/rand.(*Rand).Intn(0x400006ceb0?, 0xffff9cfa6150?)
	/usr/local/go/src/math/rand/rand.go:180 +0x64
main.genCase(0x400006ceb0)
	/home/ubuntu/codeforces/1000-1999/1600-1699/1680-1689/1682/verifierF.go:79 +0x308
main.main()
	/home/ubuntu/codeforces/1000-1999/1600-1699/1680-1689/1682/verifierF.go:138 +0x28c
exit status 2