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)

use std::io::*;
use std::str::FromStr;
use std::collections::LinkedList;

fn main() {
    let n: usize = read();
    let mut list = LinkedList::new();

    for _ in 0..n {
        let command: String = read();
        match &*command {
            "insert" => {
                let data: i32 = read();
                list.push_front(data);
            },
            "delete" => {
                let data: i32 = read();
                let mid = list.iter().position(|&x| x == data);
                if let Some(mid) = mid {
                    let mut s = list.split_off(mid);
                    s.pop_front();
                    list.append(&mut s);
                }
            },
            "deleteFirst" => {
                list.pop_front();
            },
            "deleteLast" => {
                list.pop_back();
            }
            _ => {},
        }
    }

    println!("{}", list.iter().map(|e| e.to_string()).collect::<Vec<String>>().join(" "));
}

/// 空白まで読み取り指定の型に変換する関数
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("filed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}