using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Enter an integer 'a': ");

        int num1 = Convert.ToInt32(Console.ReadLine());

        int a;

        int b;

if(int.TryParse(num1,out a) ){  

    Console.WriteLine("Enter an integer 'b': ");

        int num2 = Convert.ToInt32(Console.ReadLine());

    if(int.TryParse(Console.ReadLine(),out b)){

        Console.WriteLine("Enter operation (+, -, *, /): ");

        string oper = Console.ReadLine();

        switch(oper){

            case "-" :

            Console.WriteLine(num1-num2);

            break;

            case "+" :

            Console.WriteLine(num1+num2);

            break;

            case "*" :

            Console.WriteLine(num1*num2);

            break;

            case "/" :

            Console.WriteLine(num1/num2);

            break;

        }

}

}

    }

}