Change level after selecting a number of buttons


I am new in unity and i would really need some help with something i m stuck in.

I have 28 buttons and i want after i select 16 of them ( 16 random selectiions) to change the scene.

Please give me guidance in this.

Thank you in advance.

Have you added counter in your game?
If not , make counters first

I’ve managed to do what i wanted now i just need to limit the times you are allowed to click the buttons. But this is the code.

using UnityEngine;
using System.Collections;

public class Counter : MonoBehaviour {

	int counter=0;

	void OnGUI()
		GUI.Label (new Rect (40, 20, 200, 50), "COUNTER: " + counter); {

			if (counter >= 16) {


	void Update() {

		if (Input.GetMouseButtonDown(0))
			counter ++;