#include <bits/stdc++.h>
using namespace std;

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define FOR(i, a, b) for (int i = (a); i<(b); ++i)
#define RFOR(i, b, a) for (int i = (b)-1; i>=(a); --i)
#define MP make_pair
#define PB push_back
#define F first
#define S second
#define FILL(a, b) memset(a, b, sizeof(a))

typedef long long LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

const int INF = 1e9 + 7;

map<char, int> m;
string s[2];
VI v[2][4];
int dp[1000][1000];

string f(int l, int r, int l2, int r2)
{
	assert(r - l + 1 < 1000);
	assert(r2 - l2 + 1 < 1000);
	FOR (i, l, r + 1) FOR (j, l2, r2 + 1) dp[i - l][j - l2] = 0;
	FOR (i, l, r)
	{
		FOR (j, l2, r2)
		{
			if (s[0][i] == s[1][j])
				dp[i - l + 1][j - l2 + 1] = max(dp[i - l + 1][j - l2 + 1], dp[i - l][j - l2] + 1);	
			dp[i - l + 1][j - l2 + 1] = max(dp[i - l + 1][j - l2 + 1], dp[i - l][j - l2 + 1]);
			dp[i - l + 1][j - l2 + 1] = max(dp[i - l + 1][j - l2 + 1], dp[i - l + 1][j - l2]);
		}
	}
	string t = "";
	int x = r, y = r2;
	while (x != l && y != l2)
	{
		if (dp[x - l][y - l2] == dp[x - l - 1][y - l2 - 1] + 1 && s[0][x - 1] == s[1][y - 1])
		{
			t += s[0][x - 1];
			x--;
			y--;
			continue;
		}
		if (dp[x - l - 1][y - l2] >= dp[x - l][y - l2 - 1])
			x--;
		else
			y--;
	}
	reverse(ALL(t));
	return t;
}

void check(string str)
{
	int n = SZ(s[0]);
	int j = 0;
	FOR (t, 0, 2)
	{
		FOR (i, 0, SZ(str))
		{
			while (j < n && s[t][j] != str[i]) j++;
			
			if (j == n) assert(0);
			j++;
		}
		j = 0;
	}
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	
	m['A'] = 0;
	m['G'] = 1;
	m['T'] = 2;
	m['C'] = 3;
	
	int n;
	cin >> n;
	cin >> s[0] >> s[1];
	int l = 0;
	int x = 147;
	string ans = "";
	while (l + x <= n)
	{
		ans += f(l, l + x, l, l + x);
		l += x;
	}
	ans += f(l, n, l, n);
	cerr << SZ(ans) << '\n';
	assert(SZ(ans) * 2 >= n);
	cout << ans << '\n';	
	
	check(ans);
	
	return 0;
}