#include<stdio.h>
#include<string.h>
#define max 100
int dq[max];
int front=-1,rear=-1;
int isEmpty(){
    return(front==-1||front>rear);
}
void priority_board(int x){
    if(front==-1){
        front=rear=0;
        dq[front]=x;
    }
    else{
        front--;
        dq[front]=x;
    }
}
void general_board(int x){
    if(rear=-1){
        front=rear=0;
        dq[rear]=x;
    }
    else{
        rear++;
        dq[rear]=x;
    }
}
void board_train(){
    if(isEmpty()){
        printf("invalid operation\n");
        return;
    }
    front++;
}
void display(){
    if(isEmpty()){
        printf("no passengers\n")
        return;
    }
    for(int i=front;i<=rear;i++)
    printf("%d",dq[i]);
    printf("\n");
}
int main(){
    int N,x;
    char cmd[30];
    scanf("%d",&N);
    while(N--){
        scanf("%s",cmd);
        if(strcmp(cmd,"general_board"))
    }
}