using System;
using System.Linq;
using System.Collections.Generic;
 
public class Test
{
 
	public static void Main()
	{
         var  List1=new[] {"123456", "432978", "321675", "321675"  };
          var List2 = new[] { "7674543897", "1234568897", "8899776644" };
 
            var match = from str1 in List1
                        join str2 in List2
                        on str1 equals (str2.Length < 6 ? str2 : str2.Substring(0, 6))
                        select str2;
            foreach(string  s2 in match)Console.WriteLine(s2);
	}   
}
 
 
 

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