Redirect to specific page based on user Roles

I am using Formsauthentication. My situation is as per below:
the login form has codebehind :
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protected void LoginButton_Click(object sender, EventArgs e)
        {
            TextBox uname = Login1.FindControl("UserName") as TextBox;
            TextBox pass = Login1.FindControl("Password") as TextBox;
            CheckBox rm = Login1.FindControl("RememberMe") as CheckBox;
            Literal fail = Login1.FindControl("Literal1") as Literal;

            if (Membership.ValidateUser(uname.Text, pass.Text))
      &nb ...