Add 1 to a NumValue after surface gui click? [SOLVED] [closed]

I'm trying to make something that will Add 1 to the NumValue each time different buttons are pressed. (I'm working towards a till system) but it doesn't seem to work. There's no outputs. (I know all of the script.Parents are very in-efficient, But they do lead to the NumValue named Cost)

local cost = script.Parent.Parent.Parent.Parent.Cost

function onClick()
    script.Parent.Parent.Parent.Parent.MainMenu.Cost.Value = script.Parent.Parent.Parent.Parent.MainMenu.Cost.Value + 1

end

script.Parent.MouseButton1Click:connect(onClick)