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: Wrong Answer)

using System;
using System.Linq;
class Program
{
    public static void Main()
    {
        var acgt = new char[] { 'A', 'C', 'G', 'T' };
        var str = Console.ReadLine().Trim();
        var len = 0;
        for (int i = 0; i < str.Length; i++)
        {
            var begin = str.IndexOfAny(acgt, i);
            if(begin == -1)
            {
                break;
            }
            i = begin;
            while(i < str.Length)
            {
                if(!acgt.Any(c => c == str[i]))
                {
                    len = Math.Max(len, i - begin);
                    break;
                }
                i++;
            }
            if(i == str.Length)
            {
                len = Math.Max(len, i - begin);
            }
        }
        Console.WriteLine("{0}", len);
    }
}