panic: invalid argument to Intn

goroutine 1 [running]:
math/rand.(*Rand).Intn(0x4000076e58?, 0x3?)
	/usr/local/go/src/math/rand/rand.go:180 +0x64
main.buildTests(0x4000076e58)
	/home/ubuntu/codeforces/2000-2999/2000-2099/2040-2049/2042/verifierC.go:114 +0x100
main.main()
	/home/ubuntu/codeforces/2000-2999/2000-2099/2040-2049/2042/verifierC.go:37 +0x1e0
exit status 2