using System;

using System.Linq;

using System.Collections.Generic;

using System.Threading;

using System.Threading.Tasks;

​

public class Program

{

    public static void Main(string[] args)

    {

        decimal val = 0;

        var myvalue = 3.14159m;

        var tmp = myvalue.ToString();

        var substr = tmp.Substring(0, 3

                                  );

        var success =  decimal.TryParse(substr, out val);

        if (success)

            Console.WriteLine(val);

    }

}