#include<iostream>
#include<map>
#include<string>
#include<vector>
using namespace std;

int N;
string A, B;
vector<int> pos[2][4];

map<char,int> loc = {{'A',0},{'C',1},{'G',2},{'T',3}};

int main() {
	cin >> N >> A >> B;
	for (int i=N-1; i >= 0; i--) {
		pos[0][loc[A[i]]].push_back(i);
		pos[1][loc[B[i]]].push_back(i);
	}

	string result;
	int a = 0, b = 0;
	while (true) {
		for (int j=0; j<4; j++) {
			while (pos[0][j].back() < a) pos[0][j].pop_back();
			while (pos[1][j].back() < b) pos[1][j].pop_back();
		}
		// choose next character wisely...
		int sumskip = 1000;
		char choice = '\0';
		for (char ch : "ACGT") {
			if (pos[0][loc[ch]].empty() || pos[1][loc[ch]].empty()) continue;
			int cost = pos[0][loc[ch]].back() + pos[1][loc[ch]].back() - (a + b);
			if (cost < sumskip) {
				sumskip = cost;
				choice = ch;
			}
		}
		if (choice == '\0') {
			break;
		}
		result += choice;
		a = pos[0][loc[choice]].back() + 1;
		b = pos[1][loc[choice]].back() + 1;
	}

	cout << result << endl;
	return 0;
}