How to make a ladder script

Hi, I am trying to do a ladder script for my game, but my script dosen't work.

Is there anything wrong with this script? My player falls through the ground and stuff with this script.

Script:

 public var smooth : float;
 public var Ladder : boolean = false;
 
 
 public var newPosition : Vector3;
 
 
 
 function Awake ()
 {
     newPosition = transform.position;
     
 }
 
 
 function Update ()
 {
     PositionChanging();
     
 }
 
 
 function PositionChanging ()
 {
     var positionA : Vector3 = new Vector3(576.3549, 17.97417, 174.8432);
     var positionB : Vector3 = new Vector3(583.3901, 57.30544, 174.8432);
     
     if(Input.GetKeyDown(KeyCode.W))
         newPosition = positionA;
         
     if(Input.GetKeyDown(KeyCode.S))
         newPosition = positionB;
     
     transform.position = Vector3.Lerp(transform.position, newPosition, smooth * Time.deltaTime);
 }