1 #include<iostream>
 2 #include<vector>
 3 #include<string>
 4  
 5 using namespace std;
 6 
 7 vector<char> A, B, T;
 8 string a, b;
 9 
10 void print(vector<char> A)
11 {
12     for(int i=0;i<A.size();i++)
13         cout<<A.at(i);
14     cout<<‘\n‘;
15     T.clear();
16 }
17 
18 int bingo(vector<char> T)
19 {
20     int x = T.size();
21     for(int i=0;i<T.size()-1;i++)
22         if(T.at(x-1) == T.at(i))
23             return T.size() - i;
24     return 0;
25 }
26 
27 void fun(vector<char> A, vector<char> B, char k)
28 {
29     if(A.size() == 0 || B.size() == 0){
30         (A.size() == 0)?print(B):print(A);
31         return;
32     }
33     if(k == ‘A‘){
34         T.push_back(A.at(0));
35         A.erase(A.begin());
36         int x = bingo(T);
37         int z = x;
38         if(x){ // A 赢了 
39             int y = T.size();
40             while(x--) A.push_back(T.at(--y));
41             while(z--) T.erase(T.end()-1);
42             fun(A, B, ‘A‘);
43         }
44         else fun(A, B, ‘B‘);
45     }
46     if(k == ‘B‘){
47         T.push_back(B.at(0));
48         B.erase(B.begin());
49         int x = bingo(T);
50         int z = x;
51         if(x){ // B 赢了 
52             int y = T.size();
53             while(x--) B.push_back(T.at(--y));
54             while(z--) T.erase(T.end()-1);
55             fun(A, B, ‘B‘);
56         }
57         else fun(A, B, ‘A‘);
58     }
59 }
60 
61 int main()
62 {
63     while(cin>>a>>b)
64     {
65         for(int i=0;i<a.size();i++)
66             A.push_back(a.at(i));
67         for(int i=0;i<b.size();i++)
68             B.push_back(b.at(i));
69             
70         string c = a + b;
71         int t[100] = {0}, f = 1;
72         for(int i=0;i<c.size();i++)
73             t[(int)c.at(i)]++;
74         for(int i=48;i<100;i++)
75             if(t[i] >= 2)
76                 f = 0;
77         if(f){    // A 和 B 没有共同的牌，此时无法结束 
78             cout<<"-1"<<endl;
79             continue;
80         }
81         fun(A, B, ‘A‘);
82         A.clear();
83         B.clear();    
84     }
85     
86     getchar();
87     
88     return 0;
89 }