#include<stdio.h>
#include<string.h>
int dq[1000], f=0, r=-1;
int main() {
    int n, x;
    char cmd[20];
    scanf("%d", &n);
    while(n--){
        scanf("%s",cmd);
        if(!strcmp(cmd,"join_front")){
            scanf("%d", &x);
            dq[--f]=x;
        }

        else if(!strcmp(cmd,"join_rear")){
            scanf("%d", &x);
            dq[++r]=x;
        else if(!strcmp(cmd,"issue")){
            if(f>r)printf("Invalid operation\n");
            else f++;
        }
        else if(!strcmp(cmd,"display")){
            if(f>r)printf("No VIPs in queue\n");
            else{
                for(int i=f;i<=r;i++)
                printf("%d ",dq[i]);
                printf("\n");
            }
        }
        }  
        return 0;
    }