reference failed on test 1 (n=5): exit status 2
output:
panic: runtime error: index out of range [-1]

goroutine 1 [running]:
main.solve({0x0, 0x0})
	/tmp/cf-worker-3944988160/2081G1.go:65 +0x298
main.main()
	/tmp/cf-worker-3944988160/2081G1.go:91 +0x268