#include<stdio.h>
#include<string.h>
#define MAX 1000
int deque[MAX];
int front=-1; rear=-1;
void join_front(int x) {
    if(front == -1) 
        front=rear=0;
    else 
        front--;
        deque[front]=x;
    }
    void join_rear(int x) {
        if(rear == -1)
           front=rear=0;
        else
        rear++;
        deque[rear]=x;
    }
    void issue() {
        if(front == -1){
            printf("Invalid operation\n");
            return;
        }
        if(front == rear)
          front=rear=-1;
        else
        front++;
    }
    void display() {
        if(front == -1) {
            printf("No VIPs in queue\n");
            return;
        }
        for(int i=front;i<=rear;i++)
         printf("%d", deque[i]);
         printf("\n");
    }
    int main() {
        int n, x;
        char cmd[20];
        scanf("%d", &n);
        while(n--) {
            scanf("%s", cmd);
            if(strcmp(cmd,"join_front")==0){
                scanf("%d", &x);
                join_front(x);
            }
            else if(strcmp(cmd,"join_rear")==0){
                issue();
            }
            elseif(strcmp(cmd,"issue")==0){
                issue;
            }
            elseif(strcmp(cmd,"display")==0){
                display();
            }
        }
        return 0;
    }