c# detect excel install location in registry and open file

public void OpenInExcel(string filename)
        {
            string dir = "";
            RegistryKey key = Registry.LocalMachine;
            RegistryKey excelKey = key.OpenSubKey(@"SOFTWARE\MicroSoft\Office");
            if (excelKey != null)
            {
                foreach (string valuename in excelKey.GetSubKeyNames())
                {
                    int version = 9;
                    double currentVersion=0;
                    if (Double.TryParse(valuename, out currentVersion) && currentVersion >= version)
                    {
                        RegistryKey rootdir = excelKey.OpenSubKey(currentVersion + @".0\Excel\InstallRoot");
                        if (rootdir != null)
                        {
                            dir = rootdir.GetValue(rootdir.GetValueNames()[0]).ToString();
                            break;
                        }
                    }
                }                
            }
            if (dir != "")
            {
                ProcessStartInfo startInfo = new ProcessStartInfo();

                startInfo.FileName = dir + @"Excel.exe";
                startInfo.Arguments = "\"" + fileName + "\"";
                startInfo.UseShellExecute = false;

                using (Process process = new Process())
                {
                    process.StartInfo = startInfo;
                    try
                    {
                        process.Start();
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine("\n\nCould not start Excel process.");
                        Console.WriteLine(ex);
                    }
                }
            }
            else
            {
                MessageBox.Show("Can't Open in excel because excel is not installed.");
            }
        }