Dutor

#include<iostream>
#include<string>
using namespace std;
 
int main()
{
	string cmd;
	string stack[101] = {"http://www.acm.org/"};
	int B = 0, F = B;
	while(cin>>cmd)
	{
		switch(cmd[0])
		{
			case 'Q':
				return 0;
				break;
			case 'V':
				cin>>stack[++B];
				cout<<stack[B]<<endl;
				F = B;
				break;
			case 'B':
				if(--B < 0)
				{
					cout<<"Ignored"<<endl;
					B = 0;
				}
				else
					cout<<stack[B]<<endl;
				break;
			case 'F':
				if(++B > F)
				{
					cout<<"Ignored"<<endl;
					--B;
				}
				else
					cout<<stack[B]<<endl;
				break;
			default:
				break;
		}
	}
	return 0;
}