C++ :

#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
using namespace std;
typedef long long ll;
const ll MOD = 1000000007;
const ll P = 10000019;
const ll MAXN = 1010;
ll powP[MAXN], H1[MAXN] = {0}, H2[MAXN] = {0};
vector<pair<int, pair<int, int> > > pr1, pr2;
void init(int len) {
    powP[0] = 1;
    for(int i = 1; i <= len; i++) {
        powP[i] = (powP[i - 1] * P) % MOD;
    }
}
void calH(ll H[], string &str) {
    H[0] = str[0];
    for(int i = 1; i < str.length(); i++) {
        H[i] = (H[i - 1] * P + str[i]) % MOD;
    }
}
int calSingleSubH(ll H[], int i, int j) {
    if(i == 0) return H[j];
    return ((H[j] - H[i - 1] * powP[j - i + 1]) % MOD + MOD) % MOD;
}
void calSubH(ll H[], int len, vector<pair<int, pair<int, int> > > &pr) {
    for(int i = 0; i < len; i++) {
        for(int j = i; j < len; j++) {
            int hashValue = calSingleSubH(H, i, j);
            pr.push_back(make_pair(hashValue, make_pair(i, j)));
        }
    }
}
pair<int, int> getMax() {
    pair<int, int> ans = make_pair(0, -1);
    for(int i = 0; i < pr1.size(); i++) {
        for(int j = 0; j < pr2.size(); j++) {
            if(pr1[i].first == pr2[j].first) {
                if(pr1[i].second.second - pr1[i].second.first > ans.second - ans.first) {
                    ans = pr1[i].second;
                }
//                ans = max(ans, pr1[i].second);
            }
        }
    }
    return ans;
}
int main() {
    string str1, str2;
    getline(cin, str1);
    getline(cin, str2);
    init(max(str1.length(), str2.length()));
    calH(H1, str1);
    calH(H2, str2);
    calSubH(H1, str1.length(), pr1);
    calSubH(H2, str2.length(), pr2);
    pair<int, int> ans = getMax();
    if(ans.second - ans.first == 0) cout << "false" << endl;
    else cout << str1.substr(ans.first, ans.second - ans.first + 1) << endl;
    return 0;
}