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.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoder.Abc
{
    //https://atcoder.jp/contests/abc141/tasks/abc141_a
    public class QuestionA
    {
        public static void Main(string[] args)
        {
            var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);

            // 文字列の入力
            string s = Console.ReadLine();

            //// 整数の入力
            //long n  = long.Parse(Console.ReadLine());

            //// 文字列配列の入力
            //string[] inputStrArray = Console.ReadLine().Split(' ');

            //// 整数配列の入力
            //var inputLongArray = Console.ReadLine().Split(' ').Select(i => long.Parse(i)).ToArray();

            string result = "";

            if (s == "ABC")
            {
                result = "ARC";
            }
            else
            {
                result = "ABC";
            }

            Console.WriteLine(result);

            Console.Out.Flush();
        }
    }
}