How to obtain the username of user that invoked "run as administrator"?

int currentProcessID = Process.GetCurrentProcess().Id;
int parentID = ParentProcess.GetID(currentProcessID);
string parentOwner = ParentProcess.GetOwner(parentID);

using System;
using System.Collections.Generic;
using System.Text;
//
using System.Diagnostics;
using System.Management;

public static class ParentProcess
{
    public static int GetID(int processID)
    {
        return Process.GetProcessById(processID).Parent().Id;
    }

    public static string GetOwner(int processId)
    //From: http://stackoverflow.com/questions/777548/how-do-i-determine-the-owner-of-a-process-in-c
    {

        string query = "Select * From Win32_Process Where ProcessID = " + processId;
        ManagementObjectSearcher searcher = new ManagementObjectSearcher(query);
        ManagementObjectCollection processList = searcher.Get();

        foreach (ManagementObject obj in processList)
        {
            string[] argList = new string[] { string.Empty };
            int returnVal = Convert.ToInt32(obj.InvokeMethod("GetOwner", argList));
            if (returnVal == 0)
            {
                return argList[0];
            }
        }

        return "NO OWNER";
    }
}

//from: http://stackoverflow.com/questions/394816/how-to-get-parent-process-in-net-in-managed-way
public static class ProcessExtensions
{
    private static string FindIndexedProcessName(int pid)
    {
        var processName = Process.GetProcessById(pid).ProcessName;
        var processesByName = Process.GetProcessesByName(processName);
        string processIndexdName = null;

        for (var index = 0; index < processesByName.Length; index++)
        {
            processIndexdName = index == 0 ? processName : processName + "#" + index;
            var processId = new PerformanceCounter("Process", "ID Process", processIndexdName);
            if (processId.NextValue().Equals(pid))
            {
                return processIndexdName;
            }
        }

        return processIndexdName;
    }

    private static Process FindPidFromIndexedProcessName(string indexedProcessName)
    {
        var parentId = new PerformanceCounter("Process", "Creating Process ID", indexedProcessName);
        return Process.GetProcessById((int)parentId.NextValue());
    }

    public static Process Parent(this Process process)
    {
        return FindPidFromIndexedProcessName(FindIndexedProcessName(process.Id));
    }
}
//from: http://yacsharpblog.blogspot.com/
namespace System.Runtime.CompilerServices
{
    [AttributeUsage(
        AttributeTargets.Assembly
        | AttributeTargets.Class
        | AttributeTargets.Method,
        Inherited = false,
        AllowMultiple = false)
    ]
    public class ExtensionAttribute : Attribute
    {
    }
}