I want to stop timer when "time left" reach to zero. Any ideas ?

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

public class CountDown : MonoBehaviour

{
public float timeLeft = 10;

public Text text;
public GameObject resultsPanel;
public GameObject[] panels;
private int numberOfCorrectAnswers;
public Text resultsText;




void Update()
{
    timeLeft -= Time.deltaTime;
    text.text = "Time Left:" + Mathf.Round(timeLeft);
    

    if (timeLeft < 0)
    {
        foreach (GameObject p in panels)
        {
            p.SetActive(false);
        }
        resultsPanel.SetActive(true);
        
        displayResults();
        
    }
}

hi;
change it to this :

if (timeLeft  >= 0) 
 timeLeft -= Time.deltaTime;