task is to idetify if the given K is prime or not.
Prime number is the number that can be divided by 1 and by itself ONLY.
If given number is prime output "YES",otherwise ouput "NO".

Input:
Only one line with n number.(1<=N=<1000)
Output:
Only one line with "YES" or "NO".
Sample input 1:
4

Sample output 1:
NO

Sample input 2:
7

Sample output 2:
YES