Teleporting 2D object once

Hi have a script that moves (change the position / teleport) an object to the mouse position every time that I click but I wanted to move it only once and freeze it right there. I tried but nothing seems to work.

 using UnityEngine;
 using System.Collections;
 
 public class move : MonoBehaviour {
     
     public float speed = 1.5f;
     private Vector3 target;
     
     void Start () {
         target = transform.position;
     }
     
     void Update () {
         if (Input.GetMouseButtonDown(0)) {
             target = Camera.main.ScreenToWorldPoint(Input.mousePosition);
             target.z = transform.position.z;
 
         }
         transform.position = target;
 
     }   
 
 }