#include<stdio.h>
#include<string.h>
int main(){
    int n,dq[1000],front=500,rear=500;
    scanf("%d",&n);
    while(n--){
        char cmd[20];
        scanf("%s",cmd);
        if(strcmp(cmd,"priority_board")==0){
            int x;scanf("%d",&x);
            dq[--front]=x;
        }
        else if(strcmp(cmd,"general_board")==0){
            int x;scanf("%d",&x);
            dq[rear++]=x;
        }
        else if(strcmp(cmd,"board_train")==0){
            if(front==rear)printf("Invalid operation\n");
            else front++;
        }
        else front++;
    }
    else if(strcmp(cmd,"display")==0){
        if(front==rear)printf("No passengers\n");
        else{
            for(int i=front;i<rear;i++){
                printf("%d",dq[i]);
                if(i<rear-1)printf(" ");
            }
            printf("\n");
        }
    }
    return 0;
}