#pragma warning disable

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Runtime.Serialization.Formatters.Binary;
using System.Text;
using System.Text.RegularExpressions;


static class MainClass
{
    public static void Main(string[] args)
    {
        var b = Console.ReadLine();
        switch (b)
        {
            case "A":
                Console.WriteLine("T");
                break;
            case "G":
                Console.WriteLine("C");
                break;
            case "T":
                Console.WriteLine("A");
                break;
            case "C":
                Console.WriteLine("G");
                break;
        }


        //var n = Console.ReadLine().ToInt32();
        //var an = Console.ReadLine().SplittedStringToInt32List();
        //var counted = an.ToCountedDictionary();
        //var uncounted = 10000000;
        //var uncountedcount = 0;
        //var removing = new List<int>();

        //foreach (var item in counted)
        //{
        //    if (item.Value == 1)
        //    {
        //        uncountedcount++;
        //        removing.Add(item.Key);
        //    }
        //}
        //foreach (var item in removing)
        //{
        //    counted.Remove(item);
        //}
        //counted.Add(uncounted, uncountedcount);
        //var counted2 = counted.Select(x =>
        //{
        //    var val = 0;
        //    var key = x.Key;
        //    if (key == uncounted)
        //    {
        //        return new KeyValuePair<int, int>(uncounted, x.Value);
        //    }
        //    if (x.Value >= 3)
        //    {
        //        if (x.Value % 2 == 0)
        //        {
        //            val = x.Value / 2 - 1;
        //        }
        //        else
        //        {
        //            val = x.Value / 2;
        //        }
        //    }
        //    else
        //    {
        //        val = x.Value;
        //    }
        //    return new KeyValuePair<int, int>(key, val);
        //}).KeyValuePairListToDictionary();

    }

    public static int ParentCount;

    public static int[] Parents;
    public static int[] IfParentsChildrenCount;

    public static int[] Ranks;

    public static void InitializeUnionFind(int N)
    {
        Parents = new int[N];
        Ranks = new int[N];
        IfParentsChildrenCount = new int[N];
        for (int i = 0; i < N; i++)
        {
            Parents[i] = i;
            Ranks[i] = 0;
            IfParentsChildrenCount[i] = 1;
        }
        ParentCount = N + 1;
    }

    public static int Root(int a)
    {
        if (Parents[a] == a)
        {
            return a;
        }
        else
        {
            Parents[a] = Root(Parents[a]);
            return Parents[a];
        }
    }

    public static bool Same(int a, int b)
    {
        return Root(a) == Root(b);
    }

    public static void Unite(int a, int b)
    {
        var parentA = Root(a);
        var parentB = Root(b);
        if (parentA == parentB)
            return;
        if (Ranks[parentA] < Ranks[parentB])
        {
            Parents[parentA] = parentB;
            IfParentsChildrenCount[parentB] += IfParentsChildrenCount[parentA];
            ParentCount -= IfParentsChildrenCount[parentA];

            IfParentsChildrenCount[parentA] = 0;
        }
        else
        {
            Parents[parentB] = parentA;
            if (Ranks[parentA] == Ranks[parentB])
            {
                Ranks[parentA]++;
            }
            IfParentsChildrenCount[parentA] += IfParentsChildrenCount[parentB];
            ParentCount -= IfParentsChildrenCount[parentB];
            IfParentsChildrenCount[parentB] = 0;
        }
    }

    #region ライブラリ

    public static long ToInt64(this string str) => long.Parse(str);
    public static int ToInt32(this string str) => str == "" ? 0 : int.Parse(str);
    public static BigInteger ToBigInteger(this string str) => BigInteger.Parse(str);
    public static List<string> SplittedStringToList(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).ToList();
    public static List<int> SplittedStringToInt32List(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => int.Parse(x)).ToList();
    public static List<long> SplittedStringToInt64List(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => long.Parse(x)).ToList();
    public static List<BigInteger> SplittedStringToBigInteger(this string str) => str.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(x => BigInteger.Parse(x)).ToList();
    public const int INF = int.MaxValue / 4;
    public const long LONGINF = long.MaxValue / 2;
    public const int Mod1e9 = 1000000007;

    public static void PrintArray(char[,] array)
    {
        for (int i = 0; i < array.GetLength(0); i++)
        {
            var sb = new StringBuilder();
            for (int j = 0; j < array.GetLength(1); j++)
            {
                sb.Append(array[i, j]);
            }
            Console.WriteLine(sb.ToString());
        }
    }
    public static int Manhattan(int x1, int x2, int y1, int y2)
    {
        return Math.Abs(x1 - x2) + Math.Abs(y1 - y2);
    }

    public static Dictionary<T, int> ToCountedDictionary<T>(this IEnumerable<T> items)
    {
        var dic = new Dictionary<T, int>();
        foreach (var item in items)
        {
            if (dic.ContainsKey(item))
                dic[item]++;
            else
                dic.Add(item, 1);
        }
        return dic;
    }
    public static Dictionary<TKey,TValue> KeyValuePairListToDictionary<TKey,TValue>(this IEnumerable<KeyValuePair<TKey,TValue>> pairs)
    {
        var dic = new Dictionary<TKey, TValue>();
        foreach (var item in pairs)
        {
            dic.Add(item.Key, item.Value);
        }
        return dic;
    }

    public static long Sums(IEnumerable<int> list)
    {
        var sum = 0l;
        foreach (var item in list)
        {
            sum += item;
        }
        return sum;
        #endregion
    }

    public static int[] dx = new int[] { -1, 1, 0, 0 };
    public static int[] dy = new int[] { 0, 0, 1, -1 };

    public static int[] dxx = new int[] { 0, 1, 1, 1, 0, -1, -1, -1 };
    public static int[] dyy = new int[] { 1, 1, 0, -1, -1, -1, 0, 1 };
}



Measured memory_bytes: 11092