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 <stdio.h>
const int MAX_V = 1000000;
int main() {
	int prime[MAX_V+1];
    int i, k, v,a=0,n;
    for(i = 2; i <= MAX_V; i++) {
        prime[i] = 1;
    } 
    for(i = 2; i*i <= MAX_V; i++) {
        if(prime[i]) {
            for(k = 2 * i; k <= MAX_V; k += i) {
                prime[k] = 0;
            }
            
        } 
        
    }
    while(1){
      scanf("%d",&n);
      if(n==0)break;
      for(i=0;i<=n-2;i++){
          int isprime = prime[i];
          int isprimex = prime[i+2];
          if(isprime && isprimex){
             if(a<i)a=i;
          }
        }
        printf("%d %d\n",a,a+2);
    	a=0;
    }
    return 0; 
    
}