// editor2
#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=0;i<n;i++)
                    printf("%d",dq[i]);
                    printf("\n")
                }
    }
}
return 0;
}