#include <stdio.h>
#include <unistd.h>

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

void filter(int p) {
	int n;
	for( ; ; ) {
		read(0, &n, sizeof(n));
		if(n%p != 0)
			write(1, &n, sizeof(n));
	}
}
		/* connect stdin or stdout to pipe */
void redirect(int k, int fd[2]) {	/* k=0 or 1 */
	close(k);
	dup(fd[k]);
	close(fd[0]);
	close(fd[1]);
}

void sink() {
	int fd[2];		/* pipe file descriptors */
	int p;			/* a prime */
	for( ; ; ) {
		read(0, &p, sizeof(p));
		printf("%d\n", p);
		pipe(fd);
		if(fork()) {
			redirect(0, fd);
			continue;
		} else {	/* child process */
			redirect(1, fd);
			filter(p);
		}
	}
}

int main() {
	int fd[2];		/* pipe file descriptors */
	pipe(fd);
	if(fork()) {
		redirect(0, fd);
		sink();
	} else {		/* child process */
		redirect(1, fd);
		source();
	}
}