#include <stdio.h>
#include <string.h>

int deque[1000], front = 0, rear =-1, count = 0;

int main(){
    int n, x;
    char op[20];
    scanf("%d", &n);
    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--
            }
        }else if(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;
}