Modify the <A HREF=ex8-5.html>previous program</A> to find every prime
number less than or equal to n.
Measure how many seconds it takes to run this program.
Run this program on STU.ipv6.club.tw, and compare the running time
with your classmates.

<HR>
The algorithm may look like:
<UL>
<LI> Ask the user to input a positive number, N
<LI> Get the current time, start_time
<LI> For each number k in the range between 2 and N,
    <UL>
    <LI> if k is a prime, print k
    </UL>
<LI> Get the current time, end_time
<LI> Print out elapse_time = (start_time - end_time)
</UL>

<HR>
The program may run as follows.
<PRE>
<CODE>
Find every prime number less than or equal to N.
Please input a positive number -- <B>100</B>
2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97
It takes 0.00011 seconds to find these prime numbers.
</CODE>
</PRE>