#include <iostream>
#include <vector>
#include <iomanip>
#include <set>
#include <queue>
#include <map>
#include <string>
#include <algorithm>
#include <random>
#include <math.h>
//#pragma GCC optimize("OFast", "O3", "unroll-loops", "omit-frame-pointer", "inline");
//#pragma GCC target("sse", "sse2", "sse3", "ssse3", "sse4", popcnt, abm, mmx, avx);
//#pragma GCC option("tune=native", "arch=native", "no-zero-upper");
//#pragma clang loop vectorize_width(4) interleave_count(4);
//#pragma clang loop unroll(disable);
using namespace std;
const int INF = 1e9;
const long long mod = 1e9 + 7;
const long long lmod = 31;
const double delta = 10e-18;
vector<unsigned long long> step(1, 1);

int getNum(char num) {
	return (num - 'A' + 1);
}

unsigned long long getHash(vector<unsigned long long> & hash, int l, int r) {
	return (hash[r + 1] - (hash[l] * step[r - l + 1]));
}
int main() {
	string s1, s2;
	int nn;
	cin >> nn;
	cin >> s1;
	cin >> s2;
	vector<unsigned long long> hash1(1);
	vector<unsigned long long> hash2(1);

	for (int i = 0; i < s1.size(); i++) {
		hash1.push_back(hash1[i] * lmod + getNum(s1[i]));
		step.push_back(step[i] * lmod);
	}
	for (int i = 0; i < s2.size(); i++) {
		hash2.push_back(hash2[i] * lmod + getNum(s2[i]));
	}
	int l = 0;
	int r = hash1.size();
	while (l + 1 < r) {
		int m = (l + r) / 2;
		bool f = true;
		set<unsigned long long> se;
		for (int i = 0; i + m < hash1.size() - 1; i++) {
			se.insert(getHash(hash1, i, i + m));
		}
		for (int i = 0; i + m < hash2.size() - 1; i++) {
			if (se.find(getHash(hash2, i, i + m)) != se.end()) {
				l = m;
				f = false;
				break;
			}
		}
		if (f)
			r = m;
	}
	set<unsigned long long> se;
	for (int i = 0; i + l < hash1.size() - 1; i++) {
		se.insert(getHash(hash1, i, i + l));
	}
	int lg, rg;
	for (int i = 0; i + l < hash2.size() - 1; i++) {
		if (se.find(getHash(hash2, i, i + l)) != se.end()) {
			lg = i;
			rg = i + l;
		}
	}
	string ans;
	for (int i = lg; i <= rg; i += 1)
		ans += s2[i];
	cout << ans;
	return 0;
}