asp.net - How to get just one value from querystrig

Question

I'm write this function:

public static String QueryString(string queryStringKey)
{
    if (HttpContext.Current.Request.QueryString[queryStringKey] != null)
    {
        if (HttpContext.Current.Request.QueryString[queryStringKey].ToString() != string.Empty)
            return HttpContext.Current.Request.QueryString.GetValues(1).ToString();
    }
    return "NAQ";
}

And i want to get just one value from querystring parameter. for example i send "page" to my function and url is: "sth.com/?page=1&page=2" and function return to me: "1,2" ; but i want first value: "1", How?