panic: runtime error: index out of range [0] with length 0

goroutine 1 [running]:
main.compute({0x4000010140?, 0x4000012080?})
	/home/ubuntu/codeforces/1000-1999/1500-1599/1550-1559/1553/verifierG.go:142 +0x1920
main.generateCases()
	/home/ubuntu/codeforces/1000-1999/1500-1599/1550-1559/1553/verifierG.go:264 +0x47c
main.main()
	/home/ubuntu/codeforces/1000-1999/1500-1599/1550-1559/1553/verifierG.go:275 +0x90
exit status 2