#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--;
    }
}
    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;
}