using System;

public class Program

{

    public static void Main()

    {

        var ff = new Param.Builder().WithA("aaaa");

        var kk = ff.WithB("bbb").WithC("ccc").Build();

        Console.WriteLine(kk.A);        

        Console.WriteLine(kk.B);

        Console.WriteLine(kk.C);

​

        Console.WriteLine("Hello World");

    }

    public class Param

    {

        public string A { get; private set; }

        public string B { get; private set; }

        public string C { get; private set; }

​

      public class Builder

      {

          private string a;

          private string b;

          private string c;

          public Builder WithA(string value)

          {

              a = value;

              return this;

          }

          public Builder WithB(string value)

          {

              b = value;

              return this;

          }

          public Builder WithC(string value)

          {

              c = value;

              return this;

          }

          public Param Build()

          {

              return new Param { A = a, B = b, C = c };

          }

      }

    }

}