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

namespace ConsoleApp5
{

    class Program
    {
        static void Main(string[] args)
        {
            string str = Console.ReadLine();
            string[] S1 = str.Split(' ');
            int N = int.Parse(S1[0]);
            int Q = int.Parse(S1[1]);
            string S = Console.ReadLine();
            char[] C = new char[N];

            for(int i = 0; i < N - 1; i++)
            {
                if (S[i] == 'A' && S[i+1] == 'C')
                {
                    C[i] = 'a';
                }
                else
                {
                    C[i] = S[i];
                }
            }
            C[N-1] = S[N-1];

            int[] t = new int[N];
            for(int i = 1; i<N; i++)
            {
                if(C[i-1] == 'a')
                {
                    t[i]++;
                }
                if(i<N-1){
                	t[i+1] = t[i];
                }
            }

            for (int i = 0; i < Q; i++)
            {
                str = Console.ReadLine();
                string[] S2 = str.Split(' ');
                int l = int.Parse(S2[0]);
                int r = int.Parse(S2[1]);
                Console.WriteLine(t[r - 1] - t[l - 1]);

            }

        }
    }
}