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

main()
{
  int status;
  int mx, i, n, running, p[2];
  fd_set master, copy;

  FD_ZERO(&master);
  FD_SET(0, &master);
  mx = 0;

  running = 0;
  n = 0;

  while (1) {

    memcpy(&copy, &master, sizeof(fd_set));
    select(mx+1, &copy, NULL, NULL, NULL);

    if (FD_ISSET(0, &copy)) {           /* Read from stdin. Fork off processes later. */
      if (scanf("%d", &n) != 1 || n <= 0) exit(0);
    }

    for (i = 1; i <= mx; i++) {  /* If a child is dead, call wait() */
      if (FD_ISSET(i, &copy)) {
        wait(&status);
        FD_CLR(i, &master);
        close(i);
        running--;
      }
    }

    while (running < n) {           /* Now fork off children if necessary. */

      pipe(p);                      /* Set up the pipe */
      FD_SET(p[0], &master);
      if (p[0] > mx) mx = p[0];
      if (fork() == 0) {            /* Close all unnecessary fd's in the child */
        for (i = 0; i <= mx; i++) {
          if (FD_ISSET(i, &master)) close(i);
        }
        execlp("experiment", "experiment", NULL); exit(1); 
      }
      close(p[1]);                  /* Close the write end in the parent */
      running++;
    }
  }
}