public static void Main()
string ipString = "192.168.0.33";
string classCNetworkId = ipString.Substring(0, ipString.LastIndexOf('.'));
Console.WriteLine($"Class C Network ID: {classCNetworkId}");
classCNetworkId = String.Join('.', ipString.Split('.').Take(3));
Console.WriteLine($"Class C Network ID: {classCNetworkId}");
classCNetworkId = System.Text.RegularExpressions.Regex.Match(ipString, "^\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}").Value;
Console.WriteLine($"Class C Network ID: {classCNetworkId}");