struct node{
    char val;
    struct node *left, *right;
};
struct node *noot;
char zhongxu[30], prev[30];
void create(int zleft, int zright, int pleft,int pright,node **root){//生成树
    if(zleft > zright || pleft > pright)    return;//直接就是空啦
    int i,j;
    for(i = pleft, j = zleft;i < pright;i++,j++)    //查找分割点
        if(zhongxu[j] == prev[pleft]) break;
    (*root) = (struct node *)malloc(sizeof(struct node));   //建立节点
    node *p = *root;
    p->val = prev[pleft];
    p->left = p->right = NULL;
    create(zleft,j-1,pleft+1, i,&p->left);  //创建左子树
    create(j+1,zright,i+1,pright,&p->right);    //创建右子树
}
void hou(node *p){  //后续遍历
    if(p){
        hou(p->left);
        hou(p->right);
        putchar(p->val);
    }
}
int main(){
    scanf("%s %s",zhongxu,prev);
    node *root;
    create(0,strlen(zhongxu) - 1,0, strlen(prev) - 1,&root);
    hou(root);
}