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 ConsoleApp55
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = int.Parse(Console.ReadLine());//.Split(' ').Select(int.Parse)
            var ab = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
 
            for ( var i = 1; i< 1000; i++)
            {
                var r = check(N * i, ab);
                if (r== 1)
                {
                    Console.WriteLine("OK");
                    return;
                }
                
            }
            Console.WriteLine("NG");
 
 
 
        }
        static int  check (int c ,int[] ab ){
 
            if ( ab[1]< c)
                return -1;
            return ab[0] <= c && c <= ab[1] ? 1 :  0;
 
 
            }
    }
}