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