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;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace abc119d
{
    class Program
    {
        static void Main(string[] args)
        {
            var b = Console.Read();
            if (b == 'A')
                Console.WriteLine("T");
            else if (b == 'T')
                Console.WriteLine("A");
            else if (b == 'C')
                Console.WriteLine("G");
            else
                Console.WriteLine("C");

#if DEBUG
            Console.ReadKey();
#endif
        }

        private static bool IsRange(int a, int from, int to) => (from <= a && a <= to);
        private static int ReadInt() => int.Parse(Console.ReadLine());
        private static List<int> ReadIntList() => Console.ReadLine().Split().Select(int.Parse).ToList();
        private static double ReadDouble() => double.Parse(Console.ReadLine());
        private static List<double> ReadDoubleList() => Console.ReadLine().Split().Select(double.Parse).ToList();
        private static long ReadLong() => long.Parse(Console.ReadLine());
        private static List<long> ReadLongList() => Console.ReadLine().Split().Select(long.Parse).ToList();
        private static List<int> Int2Digits(int a) => a.ToString().ToCharArray().Select(_ => int.Parse(_.ToString())).ToList();
        private static int BinarySearch<Type>(IReadOnlyList<Type> s, Type target) // target 以下の最大要素のインデックスを返す
            where Type : IComparable
        {
            var lower = 0;
            var upper = s.Count - 1;
            while (upper - lower > 1)
            {
                var mid = lower + (upper - lower) / 2;
                if (s[mid].CompareTo(target) <= 0)
                {
                    lower = mid;
                }
                else
                {
                    upper = mid;
                }

            }
            return lower;
        }
    }
}