log.Println("Part2:", SolveSecond(data))

func SolveSecond(data []Move) int {
	var depth, fwd, aim int
	for _, d := range data {
		switch d.dir {
		case "forward":
			fwd += d.length
			depth += d.length * aim
		case "down":
			aim += d.length
		case "up":
			aim -= d.length
		default:
			panic("no way!")
		}
	}
	return depth * fwd
}