import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.SortedSet;
import java.util.TreeSet;

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
/**
 *
 * @author Ossu
 */
class DNAString {

    private final static Character[] DATASET = {'A', 'C', 'G', 'T'};
    private final static int MIN_RANGE = 0;
    private final static int MAX_RANGE = 1000;
    private final static String INVALID_CHAR = "Invalid input,not matched with dataset";
    private final static String CHAR_LENGTH_EXCEEDS = "Input does not allow to be exceeds more than " + MAX_RANGE + " characters";

    private static String returnFinalComplement(String reverseStr) {
        StringBuilder finalStr = new StringBuilder();
        for (char c : reverseStr.toCharArray()) {
            finalStr.append(
                    c == 'G' ? 'C'
                            : c == 'C' ? 'G'
                                    : c == 'T' ? 'A'
                                            : c == 'A' ? 'T'
                                                    : c
            );

        }
        return finalStr.toString();
    }
//        char[] charlist = list.toCharArray();
//        for (int i = 0; i < charlist.length; i++) {
//            switch (charlist[i]) {
//                case 'A': {
//                    charlist[i] = 'T';
//                }
//                break;
//                case 'T': {
//                    charlist[i] = 'A';
//                }
//                break;
//                case 'G': {
//                    charlist[i] = 'C';
//                }
//                break;
//                case 'C': {
//                    charlist[i] = 'G';
//                }
//                break;
//            }
//        }
//        return new String(charlist);
//
//    }

    public static boolean validateInput(String input) {
        List<Character> chars = new ArrayList<>();
        for (char c : input.toCharArray()) {
            chars.add(c);
        }
        boolean result = false;
        SortedSet<Character> mySet = new TreeSet<>(chars);
        for (int i = 0; i <= mySet.size();) {
            for (Character c : mySet) {
                result = Objects.equals(c, DATASET[i]);
                i++;
                if (!result) {
                    break;
                }
            }
            if (result) {
                return result;
            } else {
                break;
            }
        }
        return result;

    }

    public static String reverseIt(String source) {
        int i, len = source.length();
        StringBuilder dest = new StringBuilder(len);
        for (i = (len - 1); i >= 0; i--) {
            dest.append(source.charAt(i));
        }
        return dest.toString();
    }

    public static void main(String[] args) throws IOException {

        BufferedReader readInput = new BufferedReader(new InputStreamReader(System.in));
        String source = readInput.readLine();
        if (source.length() > MIN_RANGE && source.length() <= MAX_RANGE) {
            boolean validateInput = validateInput(source);
            if (validateInput) {
//                String reverseString = reverseIt(source);
                String reverseString = reverseIt(source);
                System.out.println(returnFinalComplement(reverseString));
//                String revereStringComplement = returnFinalComplement(reverseString);
            } else {
                System.out.println(INVALID_CHAR);
            }
        } else {
            System.out.println(CHAR_LENGTH_EXCEEDS);
        }
    }
}