How do I make script in C# the result will execute if all the boxes is fill up?

put a trigger on the box and colliders on the objects, and then have a script on the box that says

 void OnTriggerEnter () {
     putInBox += 1; //this is an integer
     IsTheBoxFull();
 }
 
 void IsTheBoxFull() {
     if (putInBox >= 5) {
         execute code
     } else {
         still need to put more in box
     }
 }

and then another script that lets you pick up objects and drop them into the box with the mouse

sorry for the short explanation.. the game is 3D.. my current code is like this :

void Update () {

 }
 void OnTriggerEnter(Collider other)
 {
     if (other.tag == "cube" || other.tag == "sphere")
     {
         print ("You Win!");
     }
         
     }

}

I want to make the "you win" will appear if cube and sphere is successfully placed in the box.

So in my code I use an integer where each time I count +1

and then you can just check if (integer = 2) { print ("You win!"); }