using System;
using System.Collections.Generic;
using System.Xml;

public class Test
{
	public static void Main()
	{
		var document = new XmlDocument();
            document.LoadXml(@"<Root>
      <Main Name=""Install"">
        <Details>Success</Details>
        <Maintain>Install period</Maintain>
      </Main>
    <Main Name=""Uninstall"">
        <Details>failure</Details>
        <Maintain>uninstall period</Maintain>
      </Main>
     <Main Name= ""Discard"" >
        <Details>failure</Details>
        <Maintain>discard period</Maintain>
      </Main>
     <Main Name= ""Install"" >
        <Details>Done</Details>
        <Maintain>Got Output</Maintain>
      </Main>
    </Root>");

	    Dictionary<string, bool> used = new Dictionary<string, bool>();
	
	    var allNodes = document.SelectNodes("Root/Main");
	
	    for (int i = allNodes.Count - 1; i >= 0; i--)
	    {
	        var name = ((XmlElement)allNodes[i]).GetAttribute("Name");
	
	        if (used.ContainsKey(name))
	        {
	            allNodes[i].ParentNode.RemoveChild(allNodes[i]);
	        }
	        else
	        {
	            used.Add(name, true);
	        }
	    }
	
	    Console.WriteLine(document.OuterXml);
	}
}