How do I get the XML tag's inner text and save the inner text in text file

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C#2.0

C#

C#4.0

C#3.5

OpenFileDialog openFileDialog = new OpenFileDialog();
openFileDialog.Multiselect = true;
openFileDialog.Filter = "Text files (*.txt)|*.txt|All files (*.*)|*.*";
openFileDialog.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
if (openFileDialog.ShowDialog(this) == DialogResult.OK)
{
    string strFilename = openFileDialog.FileName;
    XmlDocument xmlDoc = new XmlDocument();
    if (File.Exists(strFilename))
    {
        xmlDoc.Load(strFilename);
        string xmlFile = File.ReadAllText(strFilename);
        XmlDocument xmldoc = new XmlDocument();
        xmldoc.LoadXml(xmlFile);
        XmlNodeList nodeList = xmldoc.GetElementsByTagName("coordinates");
        string coordinates = string.Empty;
        foreach (XmlNode node in nodeList)
        {   
            coordinates = node.InnerText;
            string[] lst = coordinates.Split(" ".ToCharArray());
            foreach (string str in lst)
            {
                coordinates += str +  Environment.NewLine;
            }
        }

        SaveFileDialog savefile = new SaveFileDialog();
        savefile.Filter = "Text files (*.txt)|*.txt|All files (*.*)|*.*";
        if (savefile.ShowDialog() == DialogResult.OK)
        {
            using (StreamWriter sw = new StreamWriter(savefile.FileName))
            {
                sw.WriteLine(coordinates);
                sw.Flush();
            }
        }
    }
}

[EDIT] Added XML from Solution 1
Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2" xmlns:gx="http://www.google.com/kml/ext/2.2" xmlns:kml="http://www.opengis.net/kml/2.2" xmlns:atom="http://www.w3.org/2005/Atom">
<Document>
	<name>Untitled Path.kmz</name>
	<Style id="s_ylw-pushpin_hl">
		<IconStyle>
			<scale>1.3</scale>
			<Icon>
				<href>http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>
			</Icon>
			<hotSpot x="20" y="2" xunits="pixels" yunits="pixels"/>
		</IconStyle>
	</Style>
	<StyleMap id="m_ylw-pushpin">
		<Pair>
			<key>normal</key>
			<styleUrl>#s_ylw-pushpin</styleUrl>
		</Pair>
		<Pair>
			<key>highlight</key>
			<styleUrl>#s_ylw-pushpin_hl</styleUrl>
		</Pair>
	</StyleMap>
	<Style id="s_ylw-pushpin">
		<IconStyle>
			<scale>1.1</scale>
			<Icon>
				<href>http://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png</href>
			</Icon>
			<hotSpot x="20" y="2" xunits="pixels" yunits="pixels"/>
		</IconStyle>
	</Style>
	<Placemark>
		<name>Untitled Path</name>
		<styleUrl>#m_ylw-pushpin</styleUrl>
		<LineString>
			<tessellate>1</tessellate>
			<coordinates>
				80.4302618226675,14.10146821639644,0 80.42576847769909,14.01560482206596,0 80.42217788625582,13.94694674204649,0 80.41768407455187,13.86119299421783,0 80.39658103437603,13.79361789706296,0 80.39388165361999,13.7422419928809,0 80.390282415801,13.67377041492268,0 80.38305143626342,13.53699640691199,0 80.37760577599572,13.43454151969623,0 80.37397453710747,13.36627494143451,0 80.36943988618303,13.28097184062539,0 80.34836784687947,13.21373716074971,0 80.32456264262412,13.09546343074962,0 80.31820720889201,12.97627719905313,0 80.31364934840515,12.89121440605016,0 80.30817653247001,12.78918641302588,0 80.30360336227979,12.70421375659957,0 80.29902651922799,12.61927452126594,0 80.29443669587334,12.53437749827671,0 80.28892262385639,12.43254149390298,0 80.28616076426671,12.38164079913633,0 80.26511197822781,12.31474736051312,0 80.26050279541035,12.22995820537765,0 80.23941074889372,12.16313653744558,0 80.21645688792,12.06243774013701,0 80.17619514615069,11.96267868889682,0 80.15607602451276,11.91279853066779,0 80.11770356329768,11.84691871805963,0 80.07750416467992,11.74715799351077,0 80.02187143303681,11.6821903960103,0 79.96351572639186,11.56640475126538,0 79.94065777203802,11.4657303741187,0 79.93510632394116,11.36414102440262,0 79.92860153755805,11.24562697520951,0 79.92393943340687,11.16097451362113,0 79.91740170713379,11.04245799454426,0 79.91646313955498,11.02552624900637,0 
			</coordinates>
		</LineString>
	</Placemark>
</Document>
</kml>

What I have tried:

the o/p obtained for this code is
80.4302618226675,14.10146821639644,0 80.42576847769909,14.01560482206596,0 80.42217788625582,13.94694674204649,0 80.41768407455187,13.86119299421783,0 80.39658103437603,13.79361789706296,0 80.39388165361999,13.7422419928809,0 80.390282415801,13.67377041492268,0 80.38305143626342,13.53699640691199,0 80.37760577599572,13.43454151969623,0 80.37397453710747,13.36627494143451,0 80.36943988618303,13.28097184062539,0
80.4302618226675,14.10146821639644,0
80.42576847769909,14.01560482206596,0
80.42217788625582,13.94694674204649,0
80.41768407455187,13.86119299421783,0
80.39658103437603,13.79361789706296,0
80.39388165361999,13.7422419928809,0
80.390282415801,13.67377041492268,0
80.38305143626342,13.53699640691199,0
80.37760577599572,13.43454151969623,0
80.37397453710747,13.36627494143451,0
80.36943988618303,13.28097184062539,0

you can see here o/p which i actually need to get is this:

80.4302618226675,14.10146821639644,0
80.42576847769909,14.01560482206596,0
80.42217788625582,13.94694674204649,0
80.41768407455187,13.86119299421783,0
80.39658103437603,13.79361789706296,0
80.39388165361999,13.7422419928809,0
80.390282415801,13.67377041492268,0
80.38305143626342,13.53699640691199,0
80.37760577599572,13.43454151969623,0
80.37397453710747,13.36627494143451,0
80.36943988618303,13.28097184062539,0

but before that i dont need the top most value in horizantal manner,can someone help me to correct the code to obtain me the o/p in this manner please
o/p:
80.4302618226675,14.10146821639644,0
80.42576847769909,14.01560482206596,0
80.42217788625582,13.94694674204649,0
80.41768407455187,13.86119299421783,0
80.39658103437603,13.79361789706296,0