#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define MAX 50

int queue[MAX];
int front = 0, rear = -1;

void enqueue(int x) {
    queue[++rear] = x;
}

int dequeue() {
    if (front > rear) return -1;
    return queue[front++];
}

int main() {
    char input[1000];
    fgets(input, sizeof(input), stdin);

    char *token = strtok(input, " \n");
    int valid = 1;

    while (token) {
        if (strcmp(token, "out") == 0) {
            int box = dequeue();
            if (box == -1) {
                printf("Invalid input\n");
                valid = 0;
                break;
            }
            printf("%d\n", box);
        } else {
            /
            int num = atoi(token);
            if (num < 10 || num > 99) {
                printf("Invalid input\n");
                valid = 0;
                break;
            }
            enqueue(num);
        }
        token = strtok(NULL, " \n");
    }

    return 0;
}