1 #include<cstdio>
 2 #include<iostream>
 3 #include<string>
 4 #include<stack>
 5 using namespace std;
 6  
 7 int main()
 8 {
 9     stack<string> back,forward;
10     string now,URL;
11     back.push("http://www.acm.org/");
12     while(cin>>now)
13     {
14         if(now[0]==‘Q‘)
15             break;
16         else if(now[0]==‘V‘)
17         {
18             cin>>URL;
19             back.push(URL);
20             cout<<URL<<endl;
21             while(!forward.empty())     
22                 forward.pop();
23         }
24         else if(now[0]==‘B‘)
25         {
26             if(back.size()>1)          
27             {                        
28                 forward.push(back.top());             
29                 back.pop();
30                 cout<<back.top()<<endl;
31             }
32             else
33                 cout<<"Ignored"<<endl;
34         }
35         else
36         {
37             if(!forward.empty())
38             {  
39                 back.push(forward.top());
40                 cout<<forward.top()<<endl;
41                 forward.pop();
42             }
43             else
44                 cout<<"Ignored"<<endl;
45         }
46     }
47     return 0;
48 }