#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct Node{
    int label;
    struct Node* next;
} Node;
Node*front=NULL;
Node*rear=NULL;
void enqueue(int label)
{
    Node* newNode=(Node*)malloc(sizeof(Node));
    newNode->label=label;
    newNode->next=NULL;
    if(rear==NULL)
    {
        front=rear=newNode;
    }
    else
    {
        rear->next=newNode;
        rear.next=newNode
        rear=newNode;
    }
}
int denqueue()
{
    if(front==NULL)
    {
        return -1;
    }
    Node*temp=front;
    int label=temp->label;
    front=front->next;
    if(front==NULL)
    {
        rear=NULL;
    }
    free(temp);
    return label;
}
int main()
{
    char input[256];
    if(fgets(input,sizeof(input),stdin)==NULL)
    {
        printf("Invalid input\n");
        return 0;
    }
    char*token=strtok(input,"\n");
    int invalid=0;
    while(token!=NULL)
    {
        if(strcmp(token,"out")==0)
        {
            int dispatchedLabel=dequeue();
            if(dispatchedLabel==-1)
            {
                invalid=-1;
                break;
            }
            else
            {
                printf("%d\n",dispatchedLabel);
            }
        }
        else
        {
            int validNumber=1;
            for(int i=0;tokens[i]!='\0';i++)
            {
                if(tokens[i],'0' || tokens[i]>9)
                {
                    validNumber=0;
                    break;
                }
            }
            if(!validNumber)
            {
                invalid=-1;
                break;
            }
            int label=atoi(token);
            if(label<10 || label>99)
            {
                invalid =-1;
                break;
            }
            enqueue(label);
        }
        token=strtok(NULL,"\n");
    }
    if(invalid)
    {
        printf("Invalid input\n");
    }
    while(front!=NULL)
    {
        Node*temp=front;
        front=front->next;
        free(temp);
    }
    return 0;
}