#第四个测试没有通过

#include <iostream>
#include <vector>
#include <string>
using namespace std;
void xian(string zhong, string hou, string& qian);
int main() {
    string zhong, hou,qian;
    cin >> zhong >> hou;
    xian(zhong, hou, qian);
    cout << qian;
	return 0;
}
void xian(string zhong, string hou, string& qian) {
    string x = zhong, y = hou; string s = "";
    int root=0;
    for (char x : zhong) {
        if (x != hou[hou.size() - 1]) root++;
        else break;
    }
    qian.push_back(zhong[root]);
    if (zhong.size()==1||zhong==s) return;
    string zhong2 = x.erase(root, y.size() - 1), hou2=y.erase(root, y.size() - 1);
    if(zhong2!=s)xian(zhong2, hou2,qian);
    x = zhong; y = hou;
    string zhong3 = x.erase(0, root + 1), hou3 = y.erase(0, root);
    hou3.erase(hou3.size() - 1);
    if (zhong3 != s)xian(zhong3, hou3, qian);
}