<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" Title="Page" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server">
<p>Content</p>
<p><asp:Label runat="server" ID="ContentPageLabel" /></p>
</asp:Content>
<script runat="server">
protected override void OnPreInit(EventArgs e)
{
base.OnPreInit(e);
ContentPageLabel.Text = "Hello!";
}
</script>
try this code