using System.Linq;

using NBitcoin.DataEncoders;

using System;

public class Program

{

    public static void Main()

    {

        const string vpub = "vpub5ZU3dwgo1Y3EFq4y1wispLdzLtLMjLGQwsSJPrED8ty3K6KreFNWCw5xsMcvywPdXMFHo3z7hV4WHJBafdyTszvpFFL5RWwxv8Wo6YBQytT";

        var tpub = convertVPubToTPub(vpub);

        Console.WriteLine(tpub);

    }

    private static string convertVPubToTPub(string vpub) {

        // Convert vpub to bytes

        var data = Encoders.Base58Check.DecodeData(vpub);

​

        // Create tpub byte prefix

        var tpubPrefixBytes = Encoders.Hex.DecodeData("043587cf");

​

        // Create the tpub data by concatenating the tpub prefix and the original data without the version bytes

        var tpubData = tpubPrefixBytes.Concat(data.Skip(4)).ToArray();

​

        // Convert the tpub data to base58 string

        var tpub = Encoders.Base58Check.EncodeData(tpubData);

​

        return tpub;

    }

}