count down timer

i’d like to make count down timer that shows how many time remian. but unity said Time dose not contain a definition for ‘deltaTime’ i dont know why piz help me.

float timeLeft = 120.0f;

Text text;

void Awake ()
{
	text = GetComponent<Text> ();
}    
void Update()
{
	timeLeft -= Time.deltaTime;
	text.text = "time Left:" + timeLeft;
	if(timeLeft < 0)
	{
		Application.LoadLevel("GameOver");
	}
}

Are you named any class or variable on your code with the name “Time”?
If you have for example :

public  yourClass Time;

// or

public int Time;

// or directly the name of your script is Time

in this case, you are called your object with that name-
Try:

UnityEngine.Time.deltaTime;