#include <stdio.h>
#include <string.h>
#define M 75
#define N 110
typedef struct stack
{
	char bottom[N][M];
	int top;
}STACK;//栈的顺序储存表示
void InitStack(STACK *S);
void Push(STACK *S, char *e);
void Pop(STACK *S, char *e);
void ClearStack(STACK *S);
int StackEmpty(STACK *S);
main()
{
	STACK forward, backward;  //定义forward, backward
	char command[M], current[M];//定义字符一维数组command储存命令，current储存前页面.
	int i = 0, j;
	strcpy(current, "http://www.acm.org/");
	InitStack(&forward);//构造一个空栈forward
	InitStack(&backward);//构造一个空栈backward
	do{
		scanf("%s", command);
		if (strcmp(command, "VISIT") == 0)
		{
			Push(&backward, current);
			scanf("%s", current);
			ClearStack(&forward);
			printf("%s\n", current);
		}
		else if (strcmp(command, "BACK") == 0)
		{
			if (StackEmpty(&backward))
			{
				printf("Ignored\n");
			}
			else
			{
				Push(&forward, current);
				Pop(&backward, current); 
				printf("%s\n", current);
			}
		}
		else if (strcmp(command, "FORWARD") == 0)
		{
			if (StackEmpty(&forward))
			{
				printf("Ignored\n");
			}
			else
			{
				Push(&backward, current);
				Pop(&forward, current);
				printf("%s\n", current);
			}
		}
	}while (strcmp(command, "QUIT") != 0);
	return 0;
}
//构造空栈
void InitStack(STACK *S)
{
	S->top = -1;
}
//进栈
void Push(STACK *S, char *e)
{
	S->top++;
	strcpy(S->bottom[S->top], e);
}
//出栈
void Pop(STACK *S, char *e)
{
	strcpy(e, S->bottom[S->top]);
	S->top--;
}
//将栈置空
void ClearStack(STACK *S)
{
	S->top = -1;
}
//判断栈是否为空，为空则返回1，否则返回0
int StackEmpty(STACK *S)
{
	if (S->top == -1)
	{
		return 1;
	}
	else return 0;
}