#include <bits/stdc++.h>
using namespace std;
string s1,s2;
void f(string s1,string s2){
	if(s1.size()<=0)return;
	cout<<s2[s2.size()-1];
	int flag;
	for(int i=0;i<s1.size();i++){
		if(s1[i]==s2[s2.size()-1]){
			flag=i;break;
		}
	}
	f(s1.substr(0,flag),s2.substr(0,flag));
	f(s1.substr(flag+1,s1.size()-flag-1),s2.substr(flag,s1.size()-flag-1));
}
int main() {
	cin>>s1>>s2;
	f(s1,s2);
 	return 0;
}
已知前序或后序任一再加上中序可确定一棵二叉树
通过前/后序找出根，再根据该根和中序确定该根的两棵子树，不断递推可得到确定二叉树