How can I find all objects in scene under tag "Pickup"?

I need to have a script where it will find all the objects under the tag "Pickup" so that It can put it to this text I have saying how many you've collected so far out of total and I want it to find the total when the game starts.

using UnityEngine; strong textusing System.Collections;

 public class Player_Controller : MonoBehaviour
 {
     public float speed;
     public GUIText countText;
     public GUIText winText;
     private int count;
     void Start(){
                 count = 0;
                 SetCountText ();
                 winText.text = "";
     }
     
     void FixedUpdate()
         {
             float moveHorizontal = Input.GetAxis("Horizontal");
             float moveVertical = Input.GetAxis("Vertical");
             Vector3 movement = new Vector3(moveHorizontal, 0.0f, moveVertical);
 
             rigidbody.AddForce(movement * speed * Time.deltaTime);
         }
         void OnTriggerEnter(Collider other)
         {
             if (other.gameObject.tag == "Pickup") 
             {
                 other.gameObject.SetActive (false);
                 count = count + 1;
                 SetCountText();
             }
         }

//Below here is where I make the level complete text come up.

     void SetCountText()
     {
         countText.text = "Count: " + count.ToString ();
         if (count >= 12 //<-- I want to make a variable replace total right here. ) 
             {
             winText.text = "Level Complete";
             }
     }
 }