create a countdown timer

Timer.aspx.cs

public double seconds;

    protected void Page_Load(object sender, EventArgs e)
    {
       
                    seconds = 3600;       

    }

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Its working fine but when i click on button its strat again. So please tell me a solution while when button is clicked yet it should work continusoly not start again or not stopped.

please help me.

Thanks in advance

Pankaj