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 prime[10001];
int twin_prime[10001];

void isprime(int n) {
    int i, k, l = 0, p1, q1;
    for(i = 2; i <= n; i++) {
        prime[i] = 1;
    }
    for(i = 2; i <= n; i++) {
        if(prime[i]) {
            for(k = 2*i; k <= n; k+=i) {
                prime[k] = 0;
            }
        }
        if(prime[i]) {
            twin_prime[l] = i;
            l++;
        }
    }
    for(i = 0; i < l; i++) {
        if(twin_prime[i+1]-twin_prime[i]==2) {
            p1 = twin_prime[i];
            q1 = twin_prime[i+1];
        }
    }
    printf("%d %d\n", p1, q1);
}

int main() {
    int i, n;
    for(i = 0; i < 10000; i++) {
        scanf("%d", &n);
        if(n == 0) break;
        isprime(n);
    }
    return 0;
}