Capture Logout Time

I need to capture the logout time and login time. I can capture the login time already but I cannot capture the logout time.My logout time and login time need to be on the same entry.This is the coding in the logout button:

Code:
protected void logoutButton_Click(object sender, EventArgs e)
{
SqlCommand cmd = new SqlCommand("SELECT TOP 1 LogId FROM LoggedInUsers where MemberID = @MemberID ORDER BY LogId DESC");
cmd.Parameters.AddWithValue("@MemberID", Session["MemberID"]);
Session.Abandon();
}

I also need to do in global.asax. And this is the coding:

protected void Session_End(object sender, EventArgs e)
{
if (Session["MemberId"] != null)
{
UpdateLoggedInUsersLogoutTime(Convert.ToInt32(Session["MemberId"].ToString()));
}
//string emailaddress = (string)Session["emailaddress"];

[code]....