using System;

​

public class Program

{

    public static void Main()

    {

        int num = 8, a, b;

        while (num < 10 || num > 100)

        {

            Console.WriteLine("enter a number: ");

            num = int.Parse(Console.ReadLine());

        }

​

        a = num / 10;

        b = num % 10;

        b = b * 10;

        num = a + b;

        Console.WriteLine("opposite number: " + num);

    }

}