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 Rust (1.42.0) (judge verdict: Accepted)

//---------- Begin IO utilities ----------
#[macro_use]
#[allow(dead_code, unused_macros)]
mod io {
    // Thanks to https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
    macro_rules! input {
        ($($r:tt)*) => {
            let s = {
                use std::io::Read;
                let mut s = String::new();
                std::io::stdin().read_to_string(&mut s).unwrap();
                s
            };
            let mut iter = s.split_whitespace();
            input_inner!{iter, $($r)*}
        };
    }
    macro_rules! input_inner {
        ($iter:expr) => {};
        ($iter:expr, ) => {};
        ($iter:expr, $var:tt : $t:tt $($r:tt)*) => {
            let $var = read_value!($iter, $t);
            input_inner!{$iter $($r)*}
        };
    }
    macro_rules! read_value {
        ($iter:expr, ( $($t:tt),* )) => {
            ( $(read_value!($iter, $t)),* )
        };
        ($iter:expr, [ $t:tt ; $len:expr ]) => {
            (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
        };
        ($iter:expr, chars) => {
            read_value!($iter, String).chars().collect::<Vec<char>>()
        };
        ($iter:expr, usize1) => {
            read_value!($iter, usize) - 1
        };
        ($iter:expr, $t:ty) => {
            $iter.next().unwrap().parse::<$t>().expect("Parse error")
        };
    }

    macro_rules! p {
        ($v:expr) => {
            println!("{}", $v);
        };
        ($v:expr, $($t:expr),*) => {
            print!("{}", $v);
            ($(print!(" {}", $t)),*);
            println!();
        }
    }

    macro_rules! ps {
        ($v:expr) => {
            println!("{}", $v.iter().collect::<String>());
        };
        ($v:expr, $($t:expr),*) => {
            print!("{}", $v.iter().collect::<String>());
            ($(print!(" {}", $t.iter().collect::<String>())),*);
            println!();
        }
    }

    pub fn pv<T: std::string::ToString>(v: &[T], sep: &str) {
        let s = v.iter().map(|e| e.to_string()).collect::<Vec<String>>().join(sep);
        println!("{}", s);
    }

    pub fn pvs(v: &[Vec<char>], sep:&str) {
        let s = v.iter().map(|e| e.iter().collect::<String>()).collect::<Vec<String>>().join(sep);
        println!("{}", s);
    }
}
//---------- End IO utilities ----------

//---------- Start solve ----------
#[allow(unused_imports)]
use io::*;
fn main() {
    input!{
        s: chars
    }
    if s[1] == 'B' {
        p!("ARC");
    } else {
        p!("ABC");
    }
}