Can someone help me add running to my script?

Hi everyone I am stumped on this running bit. Im trying to add running to my script but I cant seem to make it work. Im trying to run with the left and right shift key. Please help here is the script I have for movement:

 public var MoveSpeed :float = 10;
     
     public var jumpSpeed : float = 0;
     
         public var MoveDirection = Vector3.zero;
         
             public var Gravity :float = 45;
             
                 public var grounded : boolean = false;

function Update () {

 if(grounded){
 
     MoveDirection = new Vector3(Input.GetAxis("Horizontal"), 0 , Input.GetAxis("Vertical"));
     
         MoveDirection = transform.TransformDirection(MoveDirection);
         
             MoveDirection *= MoveSpeed;
             

}

     if(grounded){
     
         if(Input.GetKey(KeyCode.Space)){
         
             MoveDirection.y = jumpSpeed;

}

}

MoveDirection.y -= Gravity * Time.deltaTime;

             var Controller = GetComponent(CharacterController);
             
                 var Flags = Controller.Move(MoveDirection * Time.deltaTime);
                 
                     grounded = (Flags & CollisionFlags.CollidedBelow) !=0;
             

}