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

#define MAX 100

int main() {
    int n;
    if (scanf("%d", &n) != 1 || n < 1 || n > 100) {
        printf("Invalid input\n");
        return 0;
    }

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

    for (int i = 0; i < n; i++) {
        char input[20];
        if (scanf("%s", input) != 1) {
            printf("Invalid input\n");
            return 0;
        }

        if (strcmp(input, "-") == 0) {
            if (count == 0) {
                printf("the chain was empty\n");
            } else {
                printf("%d\n", queue[front]);
                front = (front + 1) % MAX;
                count--;
            }
        } else {
            // Check if input is a valid nu
            for (int j = 0; input[j]; j++) {
                if (!isdigit(input[j])) {
                    printf("Invalid input\n");
                    return 0;
                }
            }

            int val = atoi(input);
            if (val < 1 || val > 1000) {
                printf("Invalid input\n");
                return 0;
            }

            if (count == MAX) {
                printf("Invalid input\n");
                return 0;
            }

            rear = (rear + 1) % MAX;
            queue[rear] = val;
            count++;
        }
    }

    return 0;
}