Score just one point per button

HI,
I would like to get one point from one button. How can I do this. Here is the script which I am using. For some reason I cant figure out how to restrict score amount.

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

public class ButtonScore1 : MonoBehaviour {
public Button yourButton;

void Start () {
	Button btn = yourButton.GetComponent<Button>();
	btn.onClick.AddListener(TaskOnClick);

}

void TaskOnClick(){
	ScoreManager.score += 1;
	Debug.Log ("You have clicked the button!");

}

}

Thanks!

It works perfectly. I will check sections you suggested before next question.