#include <iostream>#include <stack>#include <string>using namespace std;int main(){    stack<string> stack1,stack2;            string str,s1,s2;      str="http://www.acm.org/";              stack1.push(str);    while(cin>>s1){        if(s1=="QUIT")                      break;        if(s1=="VISIT"){            cin>>s2;   cout<<s2<<endl;        stack1.push(s2);              while(!stack2.empty())          stack2.pop();        } else if(s1=="BACK"){            if(stack1.size()>=2){              stack2.push(stack1.top());      stack1.pop();            cout<<stack1.top()<<endl;                } else                          puts("Ignored");          } else {            if(!stack2.empty()){                cout<<stack2.top()<<endl;                stack1.push(stack2.top());  stack2.pop();                  } else                           puts("Ignored");        }    }        return 0;}