1.

package acm_10394_twin_primes;

import java.util.Scanner;

/**
 * FWP, AusgewŠhlte Probleme aus dem ACM Programming Contest, SS10 
 * Problem: acm_10394_twin_primes
 * Link: 
 * 
 * @author Martin Lambeck
 * @version 1.0, 14.09.2010
 * 
 * Method : sieve, bitfield
 * Status : Accepted
 * Runtime: 1.656
 */


public class Main
{
	static final int intbits = 32;
	static final int MAX = 20000000;
	static int[] composed = new int[MAX/intbits + 1]; //bitfield 0 = prime, 1 = composed (wrong values for 0 and 1)
	static Scanner sc = new Scanner(System.in);
	static int[] highTwin = new int[100001];
	
	public static void main(String... args)
	{
		init();
		init2();
		
		while (sc.hasNextInt())
			testcase();
	}
	
	static void init2()
	{
		boolean prevPrime = true;
		int ind, ofs, cp;
		int pair = 0;
		
		for (int i = 5; (i <= MAX) && (pair <= 100000); i += 2)
		{
			ind = i / intbits;
			ofs = i % intbits;
			cp = (composed[ind] >> ofs) & 1;
			
			if (cp == 0)
				if (prevPrime)
				{
					highTwin[pair] = i;
					pair++;
				}
			
			prevPrime = (cp == 0);
		}
	}
	
	public static void init()
	{
		int sqrtMax = (int)Math.sqrt(MAX);
		int ind;
		int ofs;
		int cp;
		
		for (int i = 2; i <= sqrtMax; i++)
		{
			ind = i / intbits;
			ofs = i % intbits;
			cp = (composed[ind] >> ofs) & 1;
			
			if (cp == 0) //if i is prime
			{
				for (int j = i*i; j <= MAX; j += i) //all multiples of i are composed
				{
					ind = j / intbits;
					ofs = j % intbits;
					composed[ind] |= 1 << ofs; //j is composed
				}
			}
		}	
	}

	public static void testcase()
	{
		int n = sc.nextInt();
		int ht = highTwin[n-1];
		
		System.out.printf("(%d, %d)%n", ht-2, ht);
	}
}


2. 

/**
 * FWP:	Ausgewaehlte Probleme aus dem ACM (SS10)
 *
 * Method:      number theory  
 * Problem:     10394 - Twin Primes
 * Accepted:    0.972
 * @author      Evgeni Pavlidis
 *
 */

import java.io.*;
import java.util.*;

class Main {

    private static int MAX = 20000000;
    private static int HIGH = 312500;

    private static long FULL = 0xFFFFFFFFFFFFFFFFl;
    private static long MASK = 0x000000000000003Fl;

    // Bitmap of numbers.
    // isPrime[0] holds bitwise info for the numbers 0 - 63
    // isPrime[1] for 64 - 127 and so on
    private static long isPrime[] = new long[HIGH+1];
    private static int twinPrime[] = new int[1000001];


    private static void sievePrimes()
    {
        for(int i = 0; i <= HIGH; i++)
            isPrime[i] = FULL; 

        for(int i = 4; i <= MAX; i+=2)
            isPrime[i >> 6] &= ~(1l << (i & MASK));

        for(int i = 3; i <= Math.sqrt(MAX); i+=2)
            if((isPrime[i >> 6] & (1l << (i & MASK))) != 0)
                for(int j = i+i; j <= MAX; j+=i)
                    isPrime[j >> 6] &= ~(1l << (j & MASK)) ;
    }

    private static void findTwinPrimes()
    {
        int count = 1;
        for(int i = 3; i < MAX-2; i+=2)
            if( ( (isPrime[ i    >> 6] & (1l << ( i    & MASK))) != 0) &&
                ( (isPrime[(i+2) >> 6] & (1l << ((i+2) & MASK))) != 0)    )
                twinPrime[count++] = i;
    }

    public static void main(String...args) throws Exception
    {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        sievePrimes();   
        findTwinPrimes();

        String input;
        int n;
        while( (input = reader.readLine()) != null)
        {
            n = Integer.parseInt(input);
            System.out.println("(" + twinPrime[n] + ", " + (twinPrime[n]+2)+ ")");
        }
    }
}