#include <stdio.h>
#include <string.h>

#define MAX 1000

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 Operation\n");
        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]);
    }
    printf("\n");
}
int main() {
    int n;
    scanf("%d", &n);
    
    while (n--) {
        char cmd[25];
        scanf("%s", cmd);
        
        if (strcmp(cmd, "priority_board") == 0) {
            int x;
            scanf("%d", &x);
            priority_board(x);
        }
        else if (strcmp(cmd, "general_board") == 0) {
            int x;
            scanf("%d", &x);
            general_board(x);
        }
        else if (strcmp(cmd, "board_train") == 0) {
            board_train(();
        }
        else if (strcmp(cmd, "display") == 0) {
            display();
        }
    }
    return 0;
}
        }
        }
        }
        }
    }
}
    }
    }
}