Why this script is not working?

Hi,i have script,i wanted to make it that i can only press "n" button from a certain distance,but its not working,why,please check it out and help me ;(

         var myDistance: float = 20;
         var cube : GameObject;
         var jointExist : boolean;
        
         function OnCollisionEnter(c : Collision) {
      
         if(!jointExist){
      
           var joint = gameObject.AddComponent(FixedJoint);
      
           joint.connectedBody = c.rigidbody;
      
           jointExist = true;
      
        }
      
     }
        
         function Update(){
             if(Input.GetKeyDown(KeyCode.N)){
                 if(Vector3.Distance(transform.position, cube.transform.position) < myDistance){
                     if(!jointExist){
                         var joint = gameObject.GetComponent(FixedJoint);
                         Destroy(joint);
                         jointExist = false;
                     }
                 }
             }
          
         }