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