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 Rust (judge verdict: Accepted)

// ALDS1_3_C: Doubly Linked List

use std::collections::VecDeque;

fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    let n = s.trim().parse::<usize>().unwrap();

    let mut list: VecDeque<i64> = VecDeque::new();

    for _ in 0..n {
        let mut s = String::new();
        std::io::stdin().read_line(&mut s).unwrap();
        let com = s.split_whitespace().collect::<Vec<&str>>();

        match com[0] {
            "insert" => {
                let x = com[1].parse().unwrap_or(0);
                list.push_front(x);
            }
            "deleteFirst" => {
                list.pop_front();
            },
            "deleteLast" => {
                list.pop_back();
            },
            "delete" => {
                let x = com[1].parse().unwrap_or(0);
                let mut i: usize = 0;
                for y in &list {
                    if *y == x {
                        break;
                    }
                    i += 1;
                }
                list.remove(i);
            },
            _ => {
                // Do nothing.
            },
        }
    }

    let a = &list.iter()
        .map(|n| n.to_string())
        .collect::<Vec<String>>()
        .join(" ");
    println!("{}", a);
}