1. 

/**
 * FWP, Ausgewählte Probleme aus dem ACM Programming Contest, WS10/11 
 * Problem: 412 Pi
 * Link: http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=6&page=show_problem&problem=353
 * 
 * @author Fabian Liebl
 * @version 1.0, 10/06/2010
 * 
 * Method : Ad-Hoc
 * Status : Accepted
 * Runtime: 0.956
 */

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

public class Main {
	
	// Rekursive Euklid algorithm
	private static int ggT(int a, int b) {
		if (a < b) return ggT(b, a);
		if ((a == b) || (b == 0)) return a;
		return ggT(b, a%b);
	}

	public static void main(String[] args) throws IOException {
		Scanner sc = new Scanner(System.in);
		
		int numberOfValues;
		int[] values;
		int numberOfPairs;
		int numberOfCommonFactors;
		int commonFactor;
		double pi; 
		
		numberOfValues = sc.nextInt();
		while (numberOfValues != 0) {
			// Read values
			values = new int[numberOfValues];
			for (int i = 0; i < numberOfValues; i++) {
				values[i] = sc.nextInt();
			}
			
			// Check pairs
			numberOfPairs = 0;
			numberOfCommonFactors = 0;
			
			for (int firstNumber = 0; firstNumber < numberOfValues-1; firstNumber ++) {
				for (int secondNumber = firstNumber + 1; secondNumber < numberOfValues; secondNumber ++) {
					// Pair (firstNumber, secondNumber)
					numberOfPairs ++;
					if (ggT(values[firstNumber], values[secondNumber]) > 1) {
						numberOfCommonFactors ++;
					}
				}
			}
			
			if (numberOfCommonFactors == numberOfPairs) {
				System.out.println("No estimate for this data set.");
			} else {
				pi = Math.sqrt((6.0 * numberOfPairs) / (numberOfPairs - numberOfCommonFactors));
				System.out.printf("%.6f\n", pi);
			}
			
			numberOfValues = sc.nextInt();
		}
		
	}

}

2.

/**
 * FWP, Ausgewählte Probleme aus dem ACM Programming Contest, WS10/11 
 * Problem: 412 Pi
 * Link: http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=6&page=show_problem&problem=353
 * 
 * @author Manuel Hager
 * @version 1.1, 10/21/2010
 * 
 * Method : Ad-Hoc
 * Status : Accepted
 * Runtime: 0.964
 */

import java.io.IOException;
import java.util.Scanner;

public class Main
{
	public static void main(String[] args) throws IOException 
	{
		Scanner scanner = new Scanner(System.in);
		
		while(true)  
		{
			int n = scanner.nextInt();
			
			if(n == 0) {
				break;
			}
			
			int[] numbers = new int[n];
			
			for(int i = 0; i < n; i++)  {
				numbers[i] = scanner.nextInt();
			}
			
			printOut(numbers);
		}
		
		scanner.close();
	}
	
	private static void printOut(int[] values) {
		int pairCount = 0;
		int noCommonFactorCount = 0;
		
		for(int first = 0; first < values.length - 1; first++) {
			for(int second = first + 1; second < values.length; second++) {
				pairCount++;
				if(ggT(values[first], values[second]) == 1) {
					noCommonFactorCount++;
				}
			}
		}

		if(noCommonFactorCount == 0) {
			System.out.println("No estimate for this data set.");
		}
		else {
			double pi = Math.sqrt((6.0 * pairCount) / noCommonFactorCount);
			System.out.printf("%.6f%n", pi);
		}
	}
	
	private static int ggT(int a, int b){
		int r;
		do
		{
		     r = (a%b);
		     a = b;
		     b = r;
		}while(b!=0);
  
		return a;
	}
}