// editor1#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define MAX_ACTIVITIES 50
typedef struct Node 
{
    int label;
    struct Node* next;
} Node;
typedef struct 
{
    Node* front;
    Node* rear;
} Queue;
Node* createNode(int label) 
{
    Node* newNode = (Node*)malloc(sizeof(Node));
    newNode->label = label;
    newNode->next = NULL;
    return newNode;
}
void initQueue(Queue* q) 
{
    q->front = NULL;
    q->rear = NULL;
}
int isEmpty(Queue* q) 
{
    return q->front == NULL;
}
void enqueue(Queue* q, int label) 
{
    Node* newNode = createNode(label);
    if (isEmpty(q))
    {
        q->front = newNode;
        q->rear = newNode;
    } else {
        q->rear->next = newNode; 
        q->rear = newNode;
    }
}
int dequeue(Queue* q) 
{
    if (isEmpty(q)) 
    {
        return -1; 
    }
    Node* temp = q->front;
    int label = temp->label;
    q->front = q->front->next;
    if (q->front == NULL) 
    {
        q->rear = NULL;
    }
    free(temp);
    return label;
}
void freeQueue(Queue* q)
{
    while (!isEmpty(q)) 
    {
        dequeue(q);
    }
}
int main() 
{
    char input[1000];
    fgets(input, sizeof(input), stdin);
    input[strcspn(input, "\n")] = '\0';
    Queue belt;
    initQueue(&belt);
    char* token = strtok(input, " ");
    while (token != NULL) 
    {
        if (strcmp(token, "out") == 0) 
        {
            if (isEmpty(&belt)) 
            {
                printf("Invalid input\n");
                freeQueue(&belt);
                return 0;
            } 
            else
            {
                int dispatchedLabel = dequeue(&belt);
                printf("%d\n", dispatchedLabel);
            }
        } 
        else 
        {
            int isValidNumber = 1;
            for (int i = 0; token[i] != '\0'; i++)
            {
                if (!isdigit(token[i])) 
                {
                    isValidNumber = 0;
                    break;
                }
            }
            if (isValidNumber) 
            {
                int label = atoi(token);
                if (label >= 10 && label <= 99) 
                {
                    enqueue(&belt, label);
                } 
                else
                {
                    printf("Invalid input\n");
                    freeQueue(&belt);
                    return 0;
                }
            } 
            else 
            {
                printf("Invalid input\n");
                freeQueue(&belt);
                return 0;
            }
        }
        token = strtok(NULL, " ");
    }
    freeQueue(&belt);
    return 0;
}