import java.io.*;
import java.util.*;

public class MaartenSmallestLookahead {
    public static void main(String[] args) throws IOException {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            new MaartenSmallestLookahead().run(reader);
        }
    }

    public void run(BufferedReader reader) throws IOException {
        int n = Integer.parseInt(reader.readLine());
        String a = reader.readLine();
        String b = reader.readLine();
        char[] chars = "ACGT".toCharArray();
        StringBuilder out = new StringBuilder();

        int i = 0, j = 0;
        for (int k = 0; k < n / 2; k++) {
            int min = Integer.MAX_VALUE, min_i = i, min_j = 0;
            char min_c = '\0';
            for (char c : chars) {
                int x = a.indexOf(c, i);
                int y = b.indexOf(c, j);
                if (x >= i && y >= j && x + y < min) {
                    min = x + y;
                    min_c = c;
                    min_i = x + 1;
                    min_j = y + 1;
                }
            }
            out.append(min_c);
            i = min_i;
            j = min_j;
        }
        System.out.println(out);
    }
}