Help setting maxAceleration

Please help my script,,i want to make my default maxAcceleration = 5 when play, and if no input horizontal, maxacceleration going to 5 again, can you help me please ? and if i press left key, maxAcceleration not going to -10 but 0 ... please :(

 //GERAK NORMAL
 var Acceleration : float = 30;
 var maxAcceleration : float = 5;
 @HideInInspector
 var horizontalMovement : Vector2;
 
 
 function Update () 
 {
     //GERAK NORMAL
     horizontalMovement = Vector2(rigidbody.velocity.x, rigidbody.velocity.z);
     if(horizontalMovement.magnitude > maxAcceleration)
         {
             horizontalMovement = horizontalMovement.normalized;
             horizontalMovement *= maxAcceleration;
         }
     rigidbody.velocity.x = horizontalMovement.x;
     rigidbody.velocity.z = horizontalMovement.y;
 
     rigidbody.AddRelativeForce(Acceleration,0,0);
     
 }
 
 function OnGUI () 
 {
     maxAcceleration = GUI.HorizontalSlider (Rect (100, 150, 100, 10), maxAcceleration, 0, 10);
 
     maxAcceleration = Input.GetAxis("Horizontal") * 10;
     
     
 }