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 main(){
  int prime[10001];
  int i, k, n, max = 0;
  for(i = 2; i <= 10000; i++){
    prime[i] = 1;
  }
  for(i = 2; i*i <= 10000; i++){
    if(prime[i]){
      for(k = 2 * i; k <= 10000; k += i){
        prime[k] = 0;
      }
    }
  }
  while(1){ 
    scanf("%d", &n);
    if(n == 0) break;
    for(i = 2; i <= n; i++){
      if(max < i && prime[i] == 1 && prime[i-2] == 1) max = i;
    }
    printf("%d %d\n", max-2, max);
    max = 0;
  }
  return 0;
}