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: Runtime Error)

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

namespace AtCoder.Abc
{
    class QuestionE
    {
        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
            int n = int.Parse(Console.ReadLine());

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

            // 整数配列の入力
            var A = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();

            int i, j;
            int cnt = 0;

            for (i = 0; i < n; i++)
            {
                for (j = i+1 + A[i]; j < n; j++)
                {
                    if (j+1 - i+1 ==A[i] + A[i]) {
                        Console.WriteLine(i+"&"+j);
                        cnt++;
                    }
                }
            }


            Console.WriteLine(cnt);

            Console.Out.Flush();
        }
    }
}