Kill gameobject on 3rd collision?

I want to destroy the gameobject on the 3rd collision with enemy
2d game

using UnityEngine;
	using System.Collections;

	public class hok : MonoBehaviour 
	{
		public float upForce;            //upward force of the "flap"
		public float downForce;
		public float forwardSpeed;        //forward movement speed
		public bool isDead = false;        //has the player collided with a wall?

		Animator anim;                    //reference to the animator component
		bool flap = false;                //has the player triggered a "flap"?

		/*remeber the upforce +forward make large impact on style of this game  mainly the upforce so adjust accordingly and 
	 mixmatch these with gravity and mass weights under htis rb2d in inspectore*/
		void Start()
		{
			//get reference to the animator component
			anim = GetComponent<Animator> ();
			//set the bird moving forward
			GetComponent<Rigidbody2D>().velocity = new Vector2 (forwardSpeed, 0);
		}

		void Update()
		{
			//don't allow control if the bird has died
			if (isDead)
				return;
			//look for input to trigger a "flap"
			if (Input.GetKeyDown("g"))
				flap = true;
		}

		void FixedUpdate()
		{
			if (flap)
			{
				flap = false;
				anim.SetTrigger ("Flap");
				GetComponent<Rigidbody2D> ().velocity = new Vector2 (GetComponent<Rigidbody2D> ().velocity.x, 0);
				GetComponent<Rigidbody2D> ().AddForce (new Vector2 (0, upForce));
			}

			if (Input.GetKeyDown("t"))
			{
				//...zero out the dog current y velocity before...
				GetComponent<Rigidbody2D>().velocity = new Vector2(GetComponent<Rigidbody2D>().velocity.x, 0);
				GetComponent<Rigidbody2D> ().AddForce (new Vector2 (-0, downForce));
			}
		}


		void OnCollisionEnter2D(Collision2D other)
		{

			if(other.gameObject.tag == "Wall")
			{
				//if the bird collides with something set it to dead...
				//isDead = true;
				GetComponent<AudioSource>().Play();
				//...tell the animator about it...
				//anim.SetTrigger ("Die");
				//...and tell the game control about it

			}
		}

	}

Looks like all you need to do is

int hits = 0;         

void OnCollisionEnter2D(Collision2D other)
 {
        if(other.gameObject.tag == "Enemy")
        {
                  hits++;
                  if(hit >= 3)
                         Destroy(gameObject);
        }
        if(other.gameObject.tag == "Wall")
        {
                 //if the bird collides with something set it to dead...
                 //isDead = true;
                 GetComponent<AudioSource>().Play();
                 //...tell the animator about it...
                 //anim.SetTrigger ("Die");
                 //...and tell the game control about it
        }

}