Right

/// <summary>
/// Returns the last few characters of the string with a length
/// specified by the given parameter. If the string's length is less than the 
/// given length the complete string is returned. If length is zero or 
/// less an empty string is returned
/// </summary>
/// <param name="s">the string to process</param>
/// <param name="length">Number of characters to return</param>
/// <returns></returns>
public static string Right(this string s, int length)
{
    length = Math.Max(length, 0);

    if (s.Length > length)
    {
        return s.Substring(s.Length - length, length);
    }
    else
    {
        return s;
    }
}

string s = "abcde";

s = s.Right(3);   //s becomes "cde"