using System;

​

public class DotNetProgram

{

    int _a = 0;

    int _b = 0;

    int _c = 0;

    int _d = 0;

    public DotNetProgram(int a, int b)

    {

        _a = a;

        _b = b;

    }

    public DotNetProgram(int a, int b, int c, int d) : this(a, b)

    {

        _c = c;

        _d = d;

    }

    public static void Main()

    {

        DotNetProgram p = new DotNetProgram(5, 10, 15, 20);

        Console.WriteLine(p.Sum());

    }

    public int Sum()

    {

        return _a + _b + _c + _d;

    }

}