// editor3
#include<stdio.h>
#include<string.h>
#define MAX 1000
int dq[MAX];
int front=-1,rear=-1;
int isEmpty(){
    return front==-1;
}
void priority_board(int x){
    if(isEmpty()){
        front=rear=0;
    }else{
        front--;
    }
    dq[front]=x;
}
void general_board(int x){
    if(isEmpty()){
        front=rear=0;
    }else{
        rear++;
    }
    dq[rear]=x;
}
void board_train(){
    if(isEmpty()){
        printf("Invalid operation\n");
        return;
    }
    front++;
    if(front>rear){
        front=rear=-1;
    }
}
void display(){
    if(isEmpty()){
        printf("No passengers\n");
        return;
    }
    for(int i=front;i<=rear;i++){
        printf("%d",dq[i]);
        if(i<rear)
        printf("");
    }
    printf("\n");
}
int main(){
    int n,x;
    char cmd[50];
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        scanf("%s",cmd);
        if(strcmp(cmd,"priority_board")==0){
            scanf("%d",&x);
            priority_board(x);
        }
        else if(strcmp(cmd,"general_board")==0){
            scanf("%d",&x);
            general_board(x);
        }
        else if(strcmp(cmd,"board_train")==0){
            
            board_train();
        }
        else if(strcmp(cmd,"display")==0){
            display();
        }
        }
        return 0;
        }