def run(f)
    horizontal = 0
    depth = 0
    aim = 0

    f.each do |line|
        command, distance = line.split(' ')
        distance = Integer(distance)
        case command
        when 'forward'
            horizontal += distance
            depth += (aim * distance)
        when 'down'
            aim += distance
        when 'up'
            aim -= distance
        end
    end

    return horizontal * depth
end