// editor3
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<ctype.h>

#define CAPACITY 100

char queue[CAPACITY][50];
int front=0,rear=0,size=0;


void enqueue(char *packet){
    if(size==CAPACITY){
        printf("Invalid input\n");
        exit(0);
    }
    strcpy(queue[rear],packet);
    rear=(front+1)%CAPACITY;
    size--;
}

int isvalidpacket(char *s){
    if(strcmp(s," ")==0)
    return 1;
    for(int i=0;i<strlen(s);i++){
        if(!isalum(s[i]))
        return 0;
    }
    return 1;
}

int main(){
    int n;
    if(scanf("%d",&n)!=1||n<1||n>100){
        printf("Invalid input\n");
        return 0;
    }
    for(int i=;i<n;i++){
        char token[50];
        if(scanf("%s",token)!=1){
            printf("Invalid input\n");
            return 0;
        }
        if(!isvalidpacket(token)){
            printf("Invalid input\n");
            return 0;
        }
        if(strcmp(token,"-")==0){
            dequeue();
        }
        else{
            enqueue(token);
        }
    }
    return 0;
}