def run(f)
    horizontal = 0
    depth = 0

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

    return horizontal * depth
end