// editor1
#include<stdio.h>
#include<string.h>
#define max 10000
int deque [max];
int front=-1,rear=-1;
int isEmpty(){
    return front==-1;
}
void priority_board(int x){
    if(front==-1){
        front=rear=0;
    }
    else{
        front--;
    }
    deque[front]=x;
}
void general_board(int x){
    if(rear==-1){
        front=rear=0;
    }
    else{
        rear++;
    }
        deque[rear]=x;
    }
    void board_train(){
        if(isEmpty()){
            printf("Invalid operations");
            return;
        }
        if(front==rear){
            front=rear=-1;
        }
        else{
            front++;
        }
    }
    void display(){
        if(isEmpty()){
            printf("No passengers\n");
            return;
            for(int i=front;i<=rear;i++){
                printf("%d",deque[i]);
                if(i!=rear)
                printf(" ");
            }
        printf("\n");
    }
    int main(){
        int n;
        scanf("%d",&n);
        char command[30];
        int x;
        for(int i=0;i<n;i++){
            scanf("%s",command);
            if(strcmp(command,"priority_board")==0){
                scanf("%d",&x);
                priority_board(x);
            }
            else if(strcmp(command,"general_board")==0){
                scanf("%d",&x);
                general_board(x);
            }
            else if(strcmp(command,"board_train")==0){
                scanf("%d",&x);
                board_train();
            }
                else if(strcmp(command,"display")==0){
                    display();
                }
            }
            return 0;
    }