// editor1
#include<stdio.h>
#include<string.h>
int main(){
    int n,x;
    int dq[1000];
    int front=-1,rear=-1;
    char cmd[30];
    scanf("%d",&n);
    while(n--){
        scanf("%d",cmd);
        if(strcmp(cmd,"priority_board") ==0){
            scanf("%d", &x);
            if(front==-1){
            front=rear=0;
         }else{
          front--;
          }
           dq[front]=x;
        }
        else if(strcmp(cmd,"general_board") ==0){
            scanf("%d",&x);
            if(front==-1){
            front=rear=0;
            }else{
             rear++;
            }
             dq[rear]=x;
}
        else if(strcmp(cmd,"board_train") ==0){
           // scanf("%d",&x);
            if(front==-1){
        printf("Invalid operation\n");
            }
            else if(front ==rear){
               front=rear=-1; 
            }else{
                front++;
            }
}
        
        else if(strcmp(cmd,"display")==0){
            if(front==-1){
        printf("No passengers\n");
}else{
    for(int i=front;i<=rear;i++){
    printf("%d",dq[i]);
    }
       printf("\n");
}
}}
return 0;
}