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>
int data[10000];
void isprime(int n) {
    int i,k;
    for(i=2; i <=n; i++) {
        data[i] =1;
    }
    for(i=2; i*i <= n; i++) {
        if(data[i]){
            for(k=2*i;k <= n; k+=i) {
                data[k] =0;
            }
        }
    }
}
int main() {
    int i,x,Sprime=0,Lprime=0;
    while(1){
        scanf("%d",&x);
        if(x ==0)
            break;
        isprime(x);
        for(i=2; i<=x; i++){
            if(data[i] && data[i-2]){
                Sprime = i-2;
                Lprime = i;
            }
        }
        printf("%d %d\n",Sprime,Lprime);
    }
    return 0;
}