How can i add value to z ?

local player = game.Players.LocalPlayer
local RunService = game:GetService("RunService")
local ContextActionService = game:GetService("ContextActionService")

local jumping = false
local leftValue, rightValue, forwardValue, backwardValue = Vector3.new(0,0,0)

local function onBackward(actionName, inputState)
    if inputState == Enum.UserInputState.Begin then 
        backwardValue = 1
    elseif inputState == Enum.UserInputState.End then
        backwardValue = 0
    end
end

local function onForward(actionName, inputState)
    if inputState == Enum.UserInputState.Begin then 
        forwardValue = 1
    elseif inputState == Enum.UserInputState.End then
        forwardValue = 0
    end
end

local function onLeft(actionName, inputState)
    if inputState == Enum.UserInputState.Begin then 
        leftValue = 1
    elseif inputState == Enum.UserInputState.End then
        leftValue = 0
    end
end

local function onRight(actionName, inputState)
    if inputState == Enum.UserInputState.Begin then
        rightValue = 1
    elseif inputState == Enum.UserInputState.End then
        rightValue = 0
    end
end

local function onJump(actionName, inputState)
    if inputState == Enum.UserInputState.Begin then
        jumping = true
    elseif inputState == Enum.UserInputState.End then
        jumping = false
    end
end

local function onUpdate()
    if player.Character and player.Character:FindFirstChild("Humanoid") then
        if jumping then
            player.Character.Humanoid.Jump = true
        end
        local moveDirection = rightValue - leftValue - forwardValue - backwardValue
        player.Character.Humanoid:Move(Vector3.new(moveDirection,0,0,0), false)
    end
end

RunService:BindToRenderStep("Control", Enum.RenderPriority.Input.Value, onUpdate)

ContextActionService:BindAction("Forward", onForward, true, "w", Enum.KeyCode.Up, Enum.KeyCode.DPadUp)
ContextActionService:BindAction("Backward", onBackward, true, "s", Enum.KeyCode.Down, Enum.KeyCode.DPadDown)
ContextActionService:BindAction("Left", onLeft, true, "a", Enum.KeyCode.Left, Enum.KeyCode.DPadLeft)
ContextActionService:BindAction("Right", onRight, true, "d", Enum.KeyCode.Right, Enum.KeyCode.DPadRight)
ContextActionService:BindAction("Jump", onJump, true, "u", Enum.KeyCode.Up, Enum.KeyCode.DPadUp, Enum.KeyCode.ButtonA)