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