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: Time Limit Exceeded)

#include<stdio.h>

int isprime(int n){
	int i;
	for(i=2;i<n;i++){
		if(n%i==0){
			return 0;
			break;
		}
	}
	return 1;
}

int main(){
	int i,n,p1,q1;
	while(1){
		scanf("%d",&n);
		if(n==0){
			break;
		}
		if(isprime(n)==0){
			while(1){
				n--;
				if(isprime(n)==1) break;
			}
		}
		printf("deback %d\n",n);
		if(isprime(n)==1){
			p1=n;
			q1=n;
			for(i=n-1;i>0;i--){
				if(isprime(i)==1) q1=i;
				if(p1-q1==2){
					printf("%d %d\n",q1,p1);
					break;
				}else{
				p1=q1;
				}
			}
		}
	}
	return 0;
}