I need character only jump

I have a character with this script:

var speed : float = 6.0;
	var jumpSpeed : float = 8.0;
	var gravity : float = 20.0;

	private var moveDirection : Vector3 = Vector3.zero;

	function Update() {
		var controller : CharacterController = GetComponent(CharacterController);
		if (controller.isGrounded) {
			// We are grounded, so recalculate
			// move direction directly from axes
			moveDirection = Vector3(Input.GetAxis("Horizontal"), 0,
			                        Input.GetAxis("Vertical"));
			moveDirection = transform.TransformDirection(moveDirection);
			moveDirection *= speed;
			
			if (Input.GetButton ("Jump")) {
				moveDirection.y = jumpSpeed;
			}
		}

		// Apply gravity
		moveDirection.y -= gravity * Time.deltaTime;
		
		// Move the controller
		controller.Move(moveDirection * Time.deltaTime);
	}

With this code, character is moving to left and right. I need that only jump.

How to make it?

var jumpSpeed : float = 8.0;
var gravity : float = 20.0;

    private var moveDirection : Vector3 = Vector3.zero;
 
    function Update() {
       var controller : CharacterController = GetComponent(CharacterController);
       if (controller.isGrounded) {
         
 
         if (Input.GetButton ("Jump")) {
          moveDirection.y = jumpSpeed;
         }
       }
 
       // Apply gravity
       moveDirection.y -= gravity * Time.deltaTime;
 
       // Move the controller
       controller.Move(moveDirection * Time.deltaTime);
    }

Simple as that. I just removed everything unrelated to jumping.