POJ ( acm.pku.edu.cn ) 1028

#include <iostream>
#include <deque>
#include <string>
using namespace std;

int main()
{
   char instu[16]; string url;
   deque<string> b,f;
   b.push_back("http://www.acm.org/");
   while(cin>>instu){
       switch(*instu){
           case 'V':
               f.clear(); if(url!="") b.push_back(url);
               cin>>url;
               cout<<url<<endl;
               break;
           case 'B':
               if(b.empty())
                   cout<<"Ignored"<<endl;
               else {
                   f.push_back(url);
                   url=b.back();
                   b.pop_back();
                   cout<<url<<endl;
               }
               break;
           case 'F':
               if(f.empty())
                   cout<<"Ignored"<<endl;
               else {
                   b.push_back(url);
                   url=f.back();
                   f.pop_back();
                   cout<<url<<endl;
               }
               break;
           default:
               return 0;
       }
   }
   return 0;
}