Chat message to script?

I have a script, I say add 1 or add 2 or subtract 2 so on, but I have to copy & paste it every time to add a new number so I tried to make it more efficient but ended up here, with a broken script. :/

The concept is for it to add whatever the player says in chat to a surfacegui

z = game.Workspace.Part.SurfaceGui.TextBox
local function playerAdded(Player)
 Player.Chatted:connect(function(Message)

end)
if Message(1-100) then
z.Text = z.Text + Message



end

game.Players.PlayerAdded:connect(playerAdded)