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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;

// https://atcoder.jp/contests/abc122/tasks/abc122_a
namespace ADoubleHelix
{
    class Program
    {
        static void Main(string[] args)
        {
            // 入力の取得
            var inputBase = Console.ReadLine();

            char answerBase;
            switch (inputBase)
            {
                case "A":
                    answerBase = 'T';
                    break;
                case "T":
                    answerBase = 'A';
                    break;
                case "C":
                    answerBase = 'G';
                    break;
                case "G":
                    answerBase = 'C';
                    break;
                default:
                    throw new ArgumentException();
            }

            // 解答の出力
            Console.WriteLine(answerBase);
        }
    }
}