#include<stdio.h>
#include<string.h>
#define max 1000
int deque[max];
int front=max/2,rear=(max/2)-1;
int isEmpty(){
    return front>rear;
}
void pb(int x){
    if(isEmpty()){
        front=rear=0;
    }else{
        front--;
    }
    deque[front]=x;
}
void gb(int x){
    if(isEmpty()){
        front=rear=0;
    }else{
        rear++;
    }
    deque[rear]=x;
}
void bt(){
    if(isEmpty()){
        printf("Invalid operation\n");
        return;
    }
    front++;
}
void display(){
    if(isEmpty()){
        printf("No passengers\n");
        return;
    }
    for(int i=front;i<=rear;i++){
        printf("%d ",deque[i]);
    }
    printf("\n");
    }
    int main(){
        int n,x;
        char cmd[30];
        scanf("%d",&n);
        while(n--){
            scanf("%d",cmd);
            if(strcmp(cmd,"proirity_board")==0){
                scanf("%d",&x);
                pb(x);
            }else if(strcmp(cmd,"general_board")==0){
                scanf("%d",&x);
                gb(x);
            }else if(strcmp(cmd,"board_train")==0){
                bt();
            }else if(strcmp(cmd,"diaplay")==0){
                display();
}