using System;

​

public class Program

{

    public static void Main()

    {

        string testString = "abbcab";

        string Output = "";

        char[] array = testString.ToCharArray();

        for (int i = 0; i < array.Length; i++)

        {

            char l = array[i];

            char j = 'r';

            if (l == 'a')

            {

                j = 'b';

            }

​

            if (l == 'b')

            {

                j = 'a';

            }

​

            if (l == 'c')

            {

                j = ' ';

            }

​

            Output += j;

        }

​

        Console.WriteLine(Output);

    }

}