#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 MAX = 1 << 20;

int nxt[2][MAX][4];

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	string s[2];
	map<char, int> idx;
	idx['A'] = 0;
	idx['T'] = 1;
	idx['G'] = 2;
	idx['C'] = 3;
	int n;
	cin >> n;
	FOR(i, 0, 2) {
		cin >> s[i];
		FOR(j, 0, 4) {
			nxt[i][n][j] = n;
		}
		RFOR(j, n, 0) {
			FOR(k, 0, 4) {
				nxt[i][j][k] = idx[s[i][j]] == k ? j : nxt[i][j + 1][k];
			}
		}
	}
	vector<pair<int, int>> vec(n, make_pair(n, n));
	vec[0] = {-1, -1};
	FOR(d, 0, n / 2) {
		auto [i, j] = vec[d];
		FOR(k, 0, 4) {
			int ni = nxt[0][i + 1][k], nj = nxt[1][j + 1][k];
			if (ni < n && nj < n) {
				if (ni + nj < vec[d + 1].first + vec[d + 1].second) {
					vec[d + 1] = {ni, nj};
				}
			}
		}
	}
	FOR(i, 1, (n + 1) / 2 + 1) {
		assert(s[0][vec[i].first] == s[1][vec[i].second]);
		cout << s[0][vec[i].first];
	}
	cout << "\n";
	cerr << (double)clock() / CLOCKS_PER_SEC << endl;
	return 0;
}