// editor2
#include<stdio.h>
#include<string.h>
#define MAX 1000
int dq[MAX];
int front = -1,rear = -1;
int isEmpty (){
    return(front == -1 || front > rear);
}
void priority_board(int x) {
    if (front == -1) {
        front = rear = 0;
        dq[front] = x;
    }else {
        front--;
        dq[front] = x;
    }
}
void genaral_borad( int x) {
    if (rear == -1) {
        front = rear = 0;
        dq[rear] = x;
    }else {
        rear++;
        dq[rear] = x;
    }
}
void board_train() {
    if (isEmpty()) {
        printf("Invalid operation\n");
        return;
    }
    front++;
}
void display(){
    if (isEmpty()) {
        printf("No passengers");
        return;
    }
    for (int i = front; i <= rear; i++)
    printf("%d ",dq[i]);
    printf("\n");
}
int main() {
    int N, x;
    char cmd[30];
    scanf("%d", &N);
    while (N--) {
        scanf("%s", cmd);
        if (strcmp(cmd, "priority_board") == 0) {
            scanf("%d", &x);
            priority_board(x);
        }
        else if (strcmp(cmd, "genaral_board") == 0) {
            scanf("%d", &x);
            genaral_board(x);
    }
    else if (strcmp(cmd, "board_train") == 0) {
        board_train();
    }
    else if (strcmp(cmd, "display") == 0) {
        display();
    }
}
return 0;
}