#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

int
main(void)
{
    int a;
    pid_t pid = 0;
    pid = fork();
    if (pid == -1) {
        printf("-1\n");
        return 0;
    }
    if (!pid) {
        while (scanf("%d", &a) == 1) {
            pid = fork();
            if (pid == -1) {
                printf("-1\n");
                return 1;
            } else if (pid) {
                while (wait(NULL) == -1);
                printf("%d\n", a);
                _exit(0);
            }
        }
        _exit(0);
    }
    while (wait(NULL) == -1);
    return 0;
}