Problem:
Doubly Linked List

Your task is to implement a double linked list.

Write a program which performs the following operations:

insert x: insert an element with key x into the front of the list.

delete x: delete the first element which has the key of x from the list. If there is not such element, you need not do anything.

deleteFirst: delete the first element from the list.

deleteLast: delete the last element from the list.

Input

The input is given in the following format:

n

command1

command2

...

commandn

In the first line, the number of operations n is given. In the following n lines, the above mentioned operations are given in the following format:

insert x

delete x

deleteFirst

deleteLast

Output

Print all the element (key) in the list after the given operations. Two consequtive keys should be separated by a single space.

Constraints

The number of operations ≤ 2,000,000

The number of delete operations ≤ 20

0 ≤ value of a key ≤ 109

The number of elements in the list does not exceed 106

For a delete, deleteFirst or deleteLast operation, there is at least one element in the list.

Sample Input 1

7
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5

Sample Output 1

6 1 2

Sample Input 2

9
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5
deleteFirst
deleteLast

Sample Output 2

1

Solution in C (judge verdict: Accepted)

#include <stdio.h>
#define N 2000000
#define M 99
int sum[N];
int l,r;

int main(){
	int n;
	scanf("%d",&n);
	while(n--){
		char num[M];
		scanf("%s",num);
		if(num[0]=='i')scanf("%d",sum+r++);
		else if(num[6]==0){
			int t;
			scanf("%d",&t);
			for(int xu=r-1;xu>=l;xu--)if(sum[xu]==t){
				sum[xu]=-1;
				break;
			}
		}else if(num[6]=='F')while(sum[--r]==-1);
		else while(sum[l++]==-1);	
	}
	int f=0;
	for(int i=r-1;i>=l;i--)if(sum[i]!=-1)printf(f++?" %d":"%d",sum[i]);
	puts("");
}