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)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;



namespace Test1 {

    class ClassMain {
        static bool[] isPrime = Enumerable.Repeat<bool>(true,10001).ToArray();

        public static void Main(String[] args) {
            string line;
            initPrimes();
            while ((line = Console.ReadLine()) != null) {
                int n = int.Parse(line);
                if (n == 0) { break; }
                int p1 = -1, q1 = -1;
                for (int i = n; i >= 2; i--) {
                    if (isPrime[i] == false) { continue; }
                    if (isPrime[i - 2] == true) { q1 = i; p1 = i - 2; break; }
                }
                Console.WriteLine(p1 + " " + q1);
            }
        }

        public static void initPrimes() {
            isPrime[0] = false;
            isPrime[1] = false;
            for (int i = 2; i <= 10000/2; i++) {
                if (isPrime[i] == false) { continue; }
                for (int j = 2; i * j <= 10000; j++) {
                    isPrime[i * j] = false;
                }
            }
        }
    }

}