The calcuator in C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
// calcuator Program in C# (C)2018 Adm1n_0v3rride
namespace SoloLearn
{
    class Program
    {
        static void Main(string[] args)
        {
            int choice; // To choose

            int a; // For addition
            int b;
            int answer;

            int c;// For Subtraction
            int d;
            int e;

            int f; // For Multiplication
            int g;
            int h;

            int i; // For Divison
            int j;
            int k;

            Console.WriteLine("Welcome to the calcuator program v1.0\n");

            Console.WriteLine("Please Choose a Option\n");

            Console.WriteLine("1. Addition\n");

            Console.WriteLine("2. Subtraction\n");

            Console.WriteLine("3. Multiplication\n");

            Console.WriteLine("4. Divison\n");

            Console.WriteLine("Please choose: \n");

            choice = Convert.ToInt32(Console.ReadLine());

            if(choice == 1) {

                Console.WriteLine("Please input the First number: \n");

                Firstnumber = Convert.ToInt32(Console.ReadLine());

                Console.WriteLine("Please input the Secound number: \n");

                Secoundnumber = Convert.ToInt32(Console.ReadLine());

                answer = a + b;

                Console.WriteLine(" The numbers {0} and {1} equal {2} ",a,b,answer);

                Console.ReadLine();

            if(choice == 2) {

                Console.WriteLine("Please input the First number: \n");

                Firstnumber = Convert.ToInt32(Console.ReadLine());

                Console.WriteLine("Please input the Secound number: \n");

                Secoundnumber = Convert.ToInt32(Console.ReadLine());

                e = c - d;

                Console.WriteLine(" The numbers {0} and {1} equal {2} ",c,d,e);

                Console.ReadLine();

            }

            if(choice == 3) {

                Console.WriteLine("Please input the First number: \n");

                Firstnumber = Convert.ToInt32(Console.ReadLine());

                Console.WriteLine("Please input the Secound number: \n");

                Secoundnumber = Convert.ToInt32(Console.ReadLine());

                h = f * g;

                Console.WriteLine(" The numbers {0} and {1} equal {2} ",f,g,h);

                Console.ReadLine();

            }

            if(choice == 4) {

                Console.WriteLine("Please input the First number: \n");

                Firstnumber = Convert.ToInt32(Console.ReadLine());

                Console.WriteLine("Please input the Secound number: \n");

                Secoundnumber = Convert.ToInt32(Console.ReadLine());

                h = f / g;

                Console.WriteLine(" The numbers {0} and {1} equal {2} ",f,g,h);

                Console.ReadLine();

        }
    }
}