How to add rotation clamp in board tilting?

Hi, i need to add rotation clamp in the current code.

private Touch touch;

private Vector2 touchposition;

private Quaternion rotationx, rotationz;

private float tiltspeedmodifier = 0.1f;

void Update(){

if(Input.touchCount>0)
{

touch = Input.GetTouch(0);

switch(touch.phase){

case TouchPhase.Moved:

rotationx=Quaternion.Euler(
-touch.deltaPosition.x * tiltspeedmodifier,0f,0f);

transform.rotation= rotationx * transform.rotation;

rotationz= Quaternion.Euler(
0f,0f, - touch.deltaPosition.y * tiltspeedmodifier);

transform.rotation= transform.rotation * rotationz;

break;

}

}
}

Plus you need to add code tags as well.