Stop moving at the target position by using Vector3.forward

Hi I want to create a game that when I press the button, it will generates a random number and my character will move.(If the number is 3, then my character will move 3 units.) Now I have a problem. I use Vector3.forward. How to modify my script to let my character stop at the correct position? How to set the target position?

This is my script:

 var speed:float = 0.5;
 var number:int;
 static var targetPosition:Vector3; 
 var script:DiceNumber;
 var minDistance:float = 0.5;
 var a = 3;
 
 function Start () {
         script = GetComponent(DiceNumber);
         
         gameObject.Find("person4").AddComponent ("Rigidbody");
         rigidbody.constraints = RigidbodyConstraints.FreezeRotationX | 
         RigidbodyConstraints.FreezeRotationY | 
         RigidbodyConstraints.FreezeRotationZ | 
         RigidbodyConstraints.FreezePositionY;
         
 }
 
 function Go (){
         number = DiceNumber.num; //call DiceNumber.num    
         
 }
 
 function OnCollisionEnter(collision : Collision){
 
         Debug.Log("hit the" + collision.gameObject.name);
         
         if( collision.gameObject.name == "Plane10"+a){
                 rigidbody.transform.eulerAngles.y = 0;
                 
                 }        
         }
 
 public function Update () {
         
         transform.Translate(Vector3.forward * Time.deltaTime);
         
         if(Vector3.Distance(transform.position,targetPosition)< minDistance )
         animation.CrossFade("Idle");
         else
         animation.CrossFade("Walk");
         
 }

Please help me :(

Thanks!!