#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(cmp,"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;
}