#include<stdio.h>
#include<string.h>
int q[20], f=-1, r=-1;
int main(){
    int n,x,i; char c[10];
    scanf("%d",&n);
    while(n--){
        scanf("%d",c);
        if(!strcmp(c,"join_front")){
            scanf("%d",&x);
            if(f==-1) f=r=0; else f--;
            q[f]=x;
        }
        else if(!strcmp(c,"join_rear")){
            scanf("%d",&x);
            if(r==-1) f=r=0; else r++;
            q[r]=x;
        }
        else if(!strcmp(c,"issue")){
            if(f==-1) printf("Invalid operation\n");
            else if(f==r) f=r=-1;
            else f++;
        }
        else{
            if(f==-1) printf("No VIPs in queue\n");
            else{
                for(i=f;i<=r;i++)
                printf("%d ",q[i]);
                printf("\n");
            }
        }
    }
}