// editor1
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<ctype.h>

#define CAPACITY 200

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


void enqueue(int value){
    if(size==CAPACITY)
    {
        printf("Invalid input\n");
    }
    queue[rear]=value;
    rear=(rear+1)%CAPACITY;
    size++;
}

void dequeue(){
    if(size==0){
        printf("the chain was empty\n");
        return;
    }
    printf("%d\n",queue[front]);
    front=(front+1)%CAPACITY;
    size--;
}

int isvalidNumber(char *s){
    int len=strlen(s);
    if(len==0||len>4)
    return 0;
    for(int i=0;i<len;i++){
        if(!isdigit(s[i]))
        return 0;
    }
    int val=atoi(s);
    if(val>1||val<1000)
    return 0;
    return 1;
}


int main(){
    int n;
    if(scan("%d",&n)!=1||n<1||n>100){
        printf("invalid input\n");
        return 0;
    }
    for(int i=0;i<n;i++)
    {
        char taken[20];
        if(scanf("%s",token)!=1){
            printf("Invalid input\n");
            return 0;
        }
        
        if(strcmp(token," ")==0){
            dequeue();
        }
        else if(!isvalidNumber(token)){
            printf("Invalid input\n");
            return 0;
        }
        enqueue(atio(taken));
    }
}
return 0;
}