Computercraft Countdown Timer

-- Program named "startup"

local
mon = peripheral.wrap("top")
minute = ""
second = ""

term.clear()
term.setCursorPos(1, 1)

print("-~- How much time? -~-")
print(" ")

term.write("Minutes: ")
minute = read()

term.write("Seconds: ")
second = read()

if second >= 60 then -- Error here. "test:20: attempt to compare string with number expected, got string"
    print("Too many seconds. Please choose a number under 60.")
    sleep(3)
    os.reboot()
end

term.clear()
term.setCursorPos(1, 1)

while redstone.getInput("back")==false do
    term.redirect(peripheral.wrap("top"))
    mon.setTextScale(2)
    term.clear()
    term.setCursorPos(1, 1)
    print(minute..":"..second)
    sleep(.5)
    print(minute.." "..second) -- Adds blinking effect to ":"
end

if redstone.getInput("back") then
    term.redirect(peripheral.wrap("top"))

    if second < 0 then
        minute = minute-1
    end

    if second < 0 then
        second = 59
    end

    if minute==0 and second==0 then
        os.reboot()
    end

    for i = 1, 60 do
        term.redirect(peripheral.wrap("top"))
        mon.setTextScale(2)
        term.clear()
        term.setCursorPos(1, 1)
        print(minute..":"..second)
        sleep(1)

        second = second-1
    end
end