#include<iostream> #include<string> #include<stack> using namespace std; string a,url; stack<string>s1,s2; int main(){ s1.push("Ignored"); while(true){ cin>>a; if(a=="QUIT"){ break; } if(a=="VISIT"){ cin>>url; while(!s2.empty()){ s2.pop(); } s1.push(url); cout<<url<<endl; } else if(a=="BACK"){ if(s1.size()==2){ cout<<"http://www.acm.org/"<<endl; s2.push(s1.top()); s1.pop(); } else if(s1.size()==1){ cout<<"Ignored"<<endl; } else{ s2.push(s1.top()); s1.pop(); cout<<s1.top()<<endl; } } else if(a=="FORWARD"){ if(s2.size()==0){ cout<<"Ignored"<<endl; } else{ cout<<s2.top()<<endl; s1.push(s2.top()); s2.pop(); } } } return 0; }