#include <algorithm>
#include <array>
#include <cassert>
#include <iostream>
#include <optional>
#include <string>
#include <string_view>
using namespace std;

// >= 647000, 0.3s
// constexpr int lookahead = 1000;
// constexpr int width     = 100;

// >= 624000, 0.1s
constexpr int lookahead = 1000;
constexpr int width     = 10;

// >= 651000, 0.6s
// constexpr int lookahead = 5000;
// constexpr int width     = 200;

int f() {
	for(int i = 0; i < 10; ++i) {
		int j = 0;
		while(j--) ++i, cout << "HI hterasd\n";
	}
	return 0;
}

array<array<int, lookahead + 1>, lookahead + 1> dp{};
string lcs(string_view& a, string_view& b) {

	// a is the longer one
	if(a.size() < b.size()) swap(a, b);

	for(int i = 0; i < lookahead; ++i) dp[0][i] = 0, dp[i][0] = 0;

	for(int i = 0; i < a.size() and i < lookahead; ++i)
		for(int j = max(0, i - width); j < i + width and j < b.size() and j < lookahead; ++j)
			dp[i + 1][j + 1] = std::max({dp[i][j + 1], dp[i + 1][j], (a[i] == b[j]) + dp[i][j]});

	int apop = -1, bpop = -1;
	int i = min(lookahead, (int)a.size()), j = min(lookahead, (int)b.size());
	string lcs;
	if(dp[i][j] == 0) {
		a.remove_prefix(i);
		b.remove_prefix(j);
		return lcs;
	}
	while(i > 0 and j > 0) {
		if(dp[i][j] == dp[i][j - 1]) {
			--j;
			continue;
		}
		if(dp[i][j] == dp[i - 1][j]) {
			--i;
			continue;
		}
		assert(dp[i][j] == dp[i - 1][j - 1] + 1);
		assert(a[i - 1] == b[j - 1]);
		lcs.push_back(a[i - 1]);
		apop = max(apop, i);
		bpop = max(bpop, j);
		--i, --j;
	}
	a.remove_prefix(apop);
	b.remove_prefix(bpop);
	reverse(begin(lcs), end(lcs));
	return lcs;
}

int main() {

	int n;
	cin >> n;
	string as, bs;
	cin >> as >> bs;
	assert(as.size() == n and bs.size() == n);

	std::string_view a = as, b = bs;

	string ans;
	while(not a.empty() and not b.empty()) ans += lcs(a, b);
	cout << ans << endl;
	cout.flush();
}