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>
#include<string.h>

int main(){
const int MAX_V=1000000;
int prime[MAX_V+1];
	int i,k,v,n,p1,q1;
	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;
			}
		}
	}
	prime[0]=0;
	prime[1]=0;
	while(1){
		scanf("%d",&v);
		if(v==0)break;
		if(prime[v]==0){
			while(1){
				v--;
				if(prime[v]==1)break;
			}
		}
		p1=v;
		q1=v;
		for(i=v-1;i>0;i--){
			if(prime[i]==1)q1=i;
			if(p1-q1==2){
				printf("%d %d\n",q1,p1);
				break;
			}else{
				p1=q1;
			}
		}
	}
	return 0;
}