[DotNetDevelopment] how to read values from key board

[DotnetBeginner]

 I have code like this:

using System;
using System.Collections.Generic;
using System.Text;

namespace fundamentalsmethod
{
    class Test {

        public int a, b;
        public Test(int i, int j)
        {
            a = i;
            b = j;
        }
        public int change(int c)
        {
            c = a + b;
            return c;
        }
    }

    class Program
    {
        public static void Main(string[] args)
        {
            int val;
            val = int.Parse
(System.Configuration.ConfigurationManager.AppSettings["MyValue"]);
            Test ob = new Test(12,13);
            ob.change(val);
            Console.WriteLine(ob.change(val));
        }
    }

}

If i want teh sum of 30, 40 i need to change the values every time
from 12, 13 to 30. 40 what is the best way to avoid this hard code and
get the sum of any 2 nums.