This is a practice problem!

A prime number is an integer greater than 1 that is divisible only by itself and 1. Write a program that will read integers and print “yes” or “no” depending on whether or not each integer is prime.

The input to the program will be a series of integers, one per line. As a special case, if an integer is negative, the program should exit immediately without producing additional output.

Example input:

1
2
4
5
17
21
23
-1

Example output: (corresponding to the example input shown above):

no
yes
no
yes
yes
no
yes