How to reverse drag rotation?

This is the code im using to rotate my object… but i need it to rotate in reverse of the drag… the opposite direction is what i need… how would i change this?

var rotationSpeed = 10.0;
var lerpSpeed = 1.0;

private var speed = new Vector3();
private var avgSpeed = new Vector3();
private var dragging = false;
private var targetSpeedX = new Vector3();

function OnMouseDown() 
{
    dragging = true;
}

function Update () 
{

    if (Input.GetMouseButton(0) && dragging) {
        speed = new Vector3(-Input.GetAxis ("Mouse X"), Input.GetAxis("Mouse Y"), 0);
        avgSpeed = Vector3.Lerp(avgSpeed,speed,Time.deltaTime * 5);
    } else {
        if (dragging) {
            speed = avgSpeed;
            dragging = false;
        }
        var i = Time.deltaTime * lerpSpeed;
        speed = Vector3.Lerp( speed, Vector3.zero, i);   
    }

    transform.Rotate(Vector3.up, speed.x * rotationSpeed, Space.World);

}

transform.Rotate(Vector3.up, -speed.x * rotationSpeed, Space.World);

just change the sign?