231. Prime Sum

time limit per test: 0.25 sec.
memory limit per test: 4096 KB
input: standard
output: standard



Find all pairs of prime numbers (A, B) such that A<=B and their sum is also a prime number and does not exceed N.

Input
The input of the problem consists of the only integer N (1<=N<=10^6).

Output
On the first line of the output file write the number of pairs meeting the requirements. Then output all pairs one per line (two primes separated by a space).

Sample test(s)

Input
4 

Output
0  
  
  
Author:Antony Popovich 
Resource:Leningrad Regional School Programming Olympiad 
Date:January 9, 2004