#include<stdio.h>
#include<string.h>
#define MAX 100
int main()
{
    int deque[MAX];
    int size=0;
    int N;
    scanf("%d",&N);
    for(int i=0;i<N;i++)
    {
        char cmd[20];
        scanf("%s",cmd);
        if(strcmp(cmd,"join_front")==0)
        {
            int x;
            scanf("%d",&x);
            for(int j=rear;j>=front;j--)
            {
                deque[j+1]=deque[j];
            }
            deque[0]=x;
            size++;
        }
        else if(strcmp(cmd,"join_rear")==0)
        {
            int x;
            scanf("%d",&x);
            deque[size=x;
            size++;
        }
        else if(strcmp(cmd,"issue")==0)
        {
            if(size==0)
            {
                printf("Invalid operation\n");
            }
            else
            {
                for(int j=0;j<size-1;j++)
                {
                    deque[j]=deque[j+1];
                }
                size--;
            }
        }
        else if(strcmp(cmd,"display")==0)
        {
            if(size==0)
            {
                printf("No VIPs in queue\n");
            }
            else
            {
                for(int j=0;j<=size;j++)
                {
                    printf("%d",deque[j]);
                    if(j<size-1)
                        printf(" ");
                }
                printf("\n");
            }
        }
        else
        {
            printf("Invalid command\n");
        }
    }
    return 0;
}