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 Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.*;

public class Main {
    static class Reader {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader() {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1) {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.') {
                while ((c = read()) >= '0' && c <= '9') {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException {
            if (din == null)
                return;
            din.close();
        }
    }

    static class Words {
        String word;
        int cost;

        public Words(String word) {
            this.word = word;
        }
    }

    static class Node {
        int key;
        int edgeweight;

        public Node(int key, int edgeweight) {
            this.key = key;
            this.edgeweight = edgeweight;
        }
    }

    static class Graph {
        int vertices;
        ArrayList<ArrayList<Node>> al;

        public Graph(int vertices) {
            this.vertices = vertices;
            al = new ArrayList<>(vertices);
            for (int i = 0; i < vertices; i++) {
                al.add(new ArrayList<Node>());
            }
        }

        public static void addEdgeUndirected(ArrayList<ArrayList<Node>> al, int source, int destination, int weight) {
            al.get(source).add(new Node(destination, weight));
            al.get(destination).add(new Node(destination, weight));
        }
       /* public static int bfs(ArrayList<ArrayList<Node>> al, int v, int root) {
            //here root means the starting vertex for bfs
            int count = 1;
            boolean[] visited = new boolean[v];
            Queue<Integer> q = new LinkedList<>();
            visited[root] = true;
            q.add(root);
            while (!q.isEmpty()) {
                int u = q.poll();
                for (int i = 0; i < al.get(u).size(); i++) {
                    if (!visited[al.get(u).get(i).key]) {
                        visited[al.get(u).get(i).key] = true;
                        q.add(al.get(u).get(i).key);
                        count++;
                    }
                }
            }
            return count;
        }*/
       public static void bfs(ArrayList<ArrayList<Node>> al, int v, int root) {
           //here root means the starting vertex for bfs
           boolean[] visited = new boolean[v];
           Queue<Integer> q = new LinkedList<>();
           visited[root] = true;
           q.add(root);
           while (!q.isEmpty()) {
               int u = q.poll();
               System.out.print(u + " ");
               for (int i = 0; i < al.get(u).size(); i++) {
                   if (!visited[al.get(u).get(i).key]) {
                       visited[al.get(u).get(i).key] = true;
                       q.add(al.get(u).get(i).key);
                   }
               }
           }
       }

    }
    public static void main(String[] args) throws IOException {
        Reader r = new Reader();
        String s = r.readLine();
        if(s.equals("ABC")) System.out.println("ARC");
        else System.out.println("ABC");
        }
    }