Score text is generating random number

I want to add a score feature to my game, my game is clicking buttons right after it disappear but when i click the button my expection is the score text will show number instead it generate random number, How can i fix this Help

this is my scripts

ScoreScripts

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class ScoreScript : MonoBehaviour
{
public GameObject btn;

public Text ScoreText;
public int ScoreAdd;

public void Score()
{
	ScoreText.text = ScoreAdd.ToString();
	ScoreAdd++;
}

}

Button Script

using UnityEngine;
using System.Collections;
using UnityEngine.UI;
using UnityEngine.SceneManagement;

public class ButtonScript : MonoBehaviour
{
public GameObject btn;
public int destroyTime;

void Update()
{
	btn.GetComponent<Button> ().onClick.AddListener(IsClicked);
}

void IsClicked()
{
	Destroy (this.btn);
	FindObjectOfType<ScoreScript> ().Score();
}

void Start()
{
	Invoke ("nextScene", destroyTime);
}

void nextScene()
{
	SceneManager.LoadScene ("GameOver");
}

}

FIXED IT!!!

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class ScoreScript : MonoBehaviour
{
Text scoreText;
public static int scoreAdd = 0;

void Start()
{
	scoreText = GetComponent<Text> ();
}

void Update()
{
	scoreText.text = "" + scoreAdd;
}

}

using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class ButtonScript : MonoBehaviour
{
public int lifeTime;

public void onClicked()
{
	ScoreScript.scoreAdd += 1;
	Destroy (this.gameObject);
}

void Start()
{
	Invoke ("notClicked", lifeTime);
}

void notClicked()
{
	Application.LoadLevel ("GameOver");
}

}