Problem:
Score : 100 points

Problem Statement

AtCoder Inc. holds a contest every Saturday.

There are two types of contests called ABC and ARC, and just one of them is held at a time.

The company holds these two types of contests alternately: an ARC follows an ABC and vice versa.

Given a string S representing the type of the contest held last week, print the string representing the type of the contest held this week.

Constraints

S is ABC or ARC.

Input

Input is given from Standard Input in the following format:

S

Output

Print the string representing the type of the contest held this week.

Sample Input 1

ABC

Sample Output 1

ARC

They held an ABC last week, so they will hold an ARC this week.

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.IO;
using System.Text;

namespace cswork {
    class Program {
        static void Main (string[] args) {
            // string str = Util.ReadFile ();
            string str = Console.ReadLine();

            switch (str) {
                case "ABC":
                    Console.WriteLine ("ARC");
                    break;
                case "ARC":
                    Console.WriteLine ("ABC");
                    break;
            }
        }
    }

        class Util {
        public static string ReadFile () {
            StreamReader sr = new StreamReader (@"C:\data\data.txt", Encoding.UTF8);
            string str = sr.ReadToEnd ();
            sr.Close ();

            return str;
        }
    }
}