add file in sub folder share point document library

string strTopSiteUrl = System.Configuration.ConfigurationSettings.AppSettings["TopSiteURL"].ToString();
string strDocLibName = System.Configuration.ConfigurationSettings.AppSettings["DocLibName"].ToString();
string strImageFolderName = System.Configuration.ConfigurationSettings.AppSettings["ImageFolderName"].ToString();

try
{
byte[] imageData = null;
if (flUpload != null)
{
// This condition checks whether the user has uploaded a file or not
if ((flUpload.PostedFile != null) && (flUpload.PostedFile.ContentLength > 0))
{
string filename = System.IO.Path.GetFileName(flUpload.PostedFile.FileName);
string fileExtension = System.IO.Path.GetExtension(flUpload.PostedFile.FileName).ToUpper();

//This condition check for image file extesion
if (fileExtension == ".JPG" || fileExtension == ".JPEG" || fileExtension == ".BMP" || fileExtension == ".GIF")
{
Stream MyStream = flUpload.PostedFile.InputStream;
long iLength = MyStream.Length;
imageData = new byte[(int)MyStream.Length];
MyStream.Read(imageData, 0, (int)MyStream.Length);
MyStream.Close();
using (SPSite objSite = new SPSite(strTopSiteUrl))
{
using (SPWeb myWeb = objSite.OpenWeb())
{
try
{
myWeb.AllowUnsafeUpdates = true;
//SPFolder ParentFolder = myWeb.Folders[targetFolder];
string strParentFolderUrl = strTopSiteUrl + "/" + strDocLibName;
SPFolder ParentFolder = myWeb.GetFolder(strParentFolderUrl);
if (ParentFolder.SubFolders[strImageFolderName].Exists)
{
SPFolder ChildFolder = ParentFolder.SubFolders[strImageFolderName];
ChildFolder.Files.Add(filename, imageData);
string strUrl = strParentFolderUrl + "/" + strImageFolderName + "/" + filename;
myWeb.AllowUnsafeUpdates = false;
lblMessage.Text = "Uploaded successfully " + "Click Url";
}
else
{

lblMessage.Text = strImageFolderName + " already exists.";

}

}
catch (Exception ex)
{
lblMessage.Text = "An Error occured. " + ex.Message;
}

}

}
}
else
{
lblMessage.Text = "This is not valid image format.";
}
}
}
else
{
lblMessage.Text = "Please upload image";
}
}

catch (Exception ex)
{
Response.Write(ex.Message);
}