How many $$hello$$ output lines does this program print?

$1$ #include "csapp.h$"$

$2$

$3$ void doit$()$

$4\{$

$5$ Fork$()$;

$6$ Fork$()$;

$7$ printf$("$hello

$")$;

$8$ return;

$9\}$

$10$

$11$ int main$()$

$12\{$

$13$ doit$()$;

$14$ printf$("$hello

$")$;

$15$ exit$(0)$;

$16\}$