#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <assert.h>

void filter(int p)
{
    while (1)
    {
        int n;
        ssize_t nb_read = read(0, &n, sizeof(int));

        if (nb_read <= 0)
            break;

        if ((n % p) != 0)
            write(1, &n, sizeof(int));
    }
}

void seq(int n)
{
    for (int i = 2; i <= n; i++)
        write(1, &i, sizeof(int));
}

void chef(void)
{
    while (1)
    {
        int p;
        pid_t f;
        int t[2];
        ssize_t nb_read = read(0, &p, sizeof(int));

        if (nb_read <= 0)
            break;

        printf("new prime %d\n", p);
        pipe(t);
        f = fork();

        if (f == 0)
        {
            close(t[0]);
            dup2(t[1], 1);
            close(t[1]);
            filter(p);
            exit(0);
        }

        close(t[1]);
        dup2(t[0], 0);
        close(t[0]);
    }
}
int main(int argc, char *argv[])
{
    if (argc < 2)
    {
        printf("Usage: %s <N>\n", argv[0]);
        return EXIT_FAILURE;
    }

    struct sigaction sa = {0};
    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_NOCLDWAIT;
    sigaction(SIGCHLD, &sa, NULL);

    int t[2];
    int N = strtol(argv[1], NULL, 0);
    pipe(t);
    pid_t p = fork();
    assert(p != -1);

    if (p == 0)
    {
        close(t[0]);
        dup2(t[1], 1);
        close(t[1]);
        seq(N);
        exit(0);
    }

    close(t[1]);
    dup2(t[0], 0);
    close(t[0]);
    chef();
    return 0;
}