using System;
 
public class Test
{
 
private static string trimString(string str, int maxCharacters = 16) {
    if (str.Length <= maxCharacters) {
        return str;
    }
    var suffixLength = maxCharacters / 2;
    var prefixLength = maxCharacters - suffixLength;
    return string.Format(
        "{0}...{1}"
    ,   str.Substring(0, prefixLength)
    ,   str.Substring(str.Length-suffixLength, suffixLength)
    );
}
 
	public static void Main()
	{
		Console.WriteLine(trimString("123456789012", 6));
	}
}

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