local fuel = 0

term.write("Length? ")
local length = tonumber(read())

function fforward()
    while (turtle.forward() == false) do
        turtle.dig()
		sleep(0.4)
    end
    fuel = fuel + 1
end

function Chest()
	if (turtle.getItemCount(15) >= 1) then
		turtle.turnRight()
		turtle.turnRight()
		turtle.select(16)
		turtle.place()
		for i = 1, 15 do
			turtle.select(b)
			turtle.drop()
			b = b + 1
		end
		turtle.select(1)
		turtle.turnRight()
		turtle.turnRight()
	end
	b = 1
end

function Unit1()
    turtle.turnRight()
    turtle.dig()
    turtle.turnRight()
    turtle.turnRight()
    turtle.dig()
    turtle.turnRight()
end

function Unit2()
    for i = 1, length do
        if (i % 2 == 1) then do
            for j = 1, 2 do
                Chest()
                Unit1()
                turtle.digUp()
                turtle.up()
                fuel = fuel + 1
            end
            Unit1()
            fforward()
        end
        else
            for j = 1, 2 do
                Chest()
                Unit1()
                turtle.digDown()
                turtle.down()
                fuel = fuel + 1
            end
            Unit1()
            fforward()
        end
    end
end

Unit2()
print("Energy used: ")
term.write(fuel)