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: Runtime Error)

using System;

namespace c
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] N = Console.ReadLine().Split(' ');
            int Q = int.Parse(N[1]);
            string S = Console.ReadLine();
            for(int i = 0; i < Q; i++)
            {
                string[] str = Console.ReadLine().Split(' ');
                int num1 = int.Parse(str[0]);
                int num2 = int.Parse(str[1]);
                string mondai = S.Substring(num1 - 1, num2 - num1 + 1);
                Console.WriteLine(CountOf(mondai,"AC"));

            }
        }
        public static int CountOf(string target, string strArray)
        {
            int count = 0;
            int index = target.IndexOf (strArray, 0);
            while (index != -1) {
                count++;
                index = target.IndexOf (strArray, index + strArray.Length);
            }
            return count;
        }  
    }
}