Computercraft Bridge builder turtle program

function bridge()
selslot = 0
if not turtle.detectDown() then
selslot = 0
for i=1,16 do
selslot = selslot+1
turtle.select(selslot)
icount = turtle.getItemCount()
if icount >= 1 == true then
local item = turtle.getItemDetail()
if item.name == "minecraft:cobblestone" or item.name == "minecraft:dirt" or item.name == "minecraft:stone" then
turtle.placeDown()
break
end
end
end
end
end