version number comparison in c#

versionnocomp.cs

//Version 1       Version 2   Result
//1.11.17         2.3.5          2.3.5
//2.1             2.1.3          2.1.3
//2.3.5           2.4            2.4.0
//3.1             2.4            3.1.0
//3.3             3.2.9          3.3.0
//7.2.71          7.2.71         7.2.71


 string s1 = "2.1";
 string s2 = "2.11.3";

 var cnt1 = s1.Count(x => x == '.');
 if (cnt1 < 1)
     s1 = s1 + ".0";

 var cnt2 = s2.Count(x => x == '.');
 if (cnt2 < 1)
     s2 = s2 + ".0";

 var lst1 = s1.Split('.').ToList(); ;
 var lst2 = s2.Split('.').ToList(); ;
 var lst3 = new List<string>();
 lst1.ForEach(x => lst3.Add(x));
 lst2.ForEach(x => lst3.Add(x));

 string longest = lst3.OrderByDescending(s => s.Length).First();

 string s3 = string.Empty;
 foreach (var i in lst1)
 {
     s3 = s3 + i.PadLeft(longest.Length, '0') + ".";
 }

 string s4 = string.Empty;
 foreach (var i in lst2)
 {
     s4 = s4 + i.PadLeft(longest.Length, '0') + ".";
 }

 List<string> lst = new List<string> { s3, s4 };
 var res1 = lst.OrderByDescending(x => x).First();

 Console.WriteLine(res1.Remove(res1.Length-1));