Problem:
Twin Prime

Prime numbers are widely applied for cryptographic and communication technology.
A twin prime is a prime number that differs from another prime number by 2.
For example, (5, 7) and (11, 13) are twin prime pairs.

In this problem, we call the greater number of a twin prime "size of the twin prime."

Your task is to create a program which reads an integer n and prints a twin prime which has the maximum size among twin primes less than or equals to n

You may assume that 5 ≤ n ≤ 10000.

Input

The input is a sequence of datasets. The end of the input is indicated by a line containing one zero. Each dataset is formatted as follows:

n (integer)

Output

For each dataset, print the twin prime p and q (p < q). p and q should be separated by a single space.

Sample Input

12
100
200
300
0

Output for the Sample Input

5 7
71 73
197 199
281 283

Solution in C++ (judge verdict: Accepted)

#include <iostream>
#include <memory.h>
using namespace std;

#define rep(i, n) for(int i = 0; i < n; i++)

const int sz = 100000;
bool prime[sz];

int main(){
  memset(prime, true, sizeof(prime));
  prime[0] = prime[1] = false;
  for(int i = 2; i * i < sz; i++){
    if(prime[i]){
      for(int j = 2; i * j < sz; j++){
	prime[i*j] = false;
      }
    }
  }
  
  int n;
  while(cin >> n && n){
    for(int i = n; i >= 2; i--){
      if(prime[i] && prime[i-2]){
	cout << i - 2 << " " << i << endl;
	break;
      }
    }
  }
  return 0;
}