Problem:
Score : 100 points

Problem Statement

On the Planet AtCoder, there are four types of bases: A, C, G and T. A bonds with T, and C bonds with G.

You are given a letter b as input, which is A, C, G or T. Write a program that prints the letter representing the base that bonds with the base b.

Constraints

b is one of the letters A, C, G and T.

Input

Input is given from Standard Input in the following format:

b

Output

Print the letter representing the base that bonds with the base b.

Sample Input 1

A

Sample Output 1

T

Sample Input 2

G

Sample Output 2

C

Solution in Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.util.*;
public class Main {

	/*
	 * 122A
	 * 
	 * To read a character we can read it as a string and do .charAt(0) for it to be a character
	 * A <--> T
	 * C <--> G
	 * When you get one character output the other one
	 * Can be done with if statements like below
	 * 
	 * Time Complexity O(1), Memory Complexity O(1)
	 */
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		if(s.charAt(0) == 'A') {
			System.out.println('T');
		}
		else if(s.charAt(0) == 'T') {
			System.out.println('A');
		}
		else if(s.charAt(0) == 'G') {
			System.out.println('C');
		}
		else {
			System.out.println('G');
		}
	}

}