C# -Inheritance Working

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace LABexam
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        public class InputNumbers
        {
            int num1;
            int num2;

        }
        public class Addition : InputNumbers
        {
            int Anum1;
            int Anum2;
            int sum;

            Form1 f = new Form1();
            public void getSum(int x, int y)
            {
                Anum1 = x;
                Anum2 = y;

            }
            public int printSum()
            {
                sum = Anum1 + Anum2;
                return sum;
            }
        }
        public Label lbl_disp
        {
            get
            {
                return label1;
            }
        }
        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            int x;
            int y;
            x = Convert.ToInt16(textBox1.Text);
            y = Convert.ToInt16(textBox2.Text);
            Addition a = new Addition();
            a.getSum(x, y);
            label1.Text = Convert.ToString(a.printSum());
        }
    }
}