1. 



/**
* Angewandte Mathematik, SS09, IFB 2C
* ACM Problem #412 (Pi)
* Link: http://icpcres.ecs.baylor.edu/onlinejudge/index.php?option=com_onlinejudge&Itemid=8&category=23&page=show_problem&problem=136
*
* @author Fabian Seidl
* @author Marcel Sachse
* @version 1.0, 30/03/2009
*
* Status : Accepted
* Runtime: 1.240
*/

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


public class Main {

public static void main(String[] args) throws Exception
{
BufferedInputStream bInput = new BufferedInputStream(System.in);
Scanner scanner = new Scanner(bInput);

int length; // l¦nge des Datensatzes

while((length = scanner.nextInt()) != 0) // Schleife f¾r Datens¦tze
{
int[] dataSet = new int[length];

// Datensatz lesen
for(int i=0;i<length;i++)
{
dataSet[i] = scanner.nextInt();
}

int numberOfPairs = (length*length-length)/2;

int noGTcount = 0;

// Paare bilden
for(int a=0;a<length;a++)
{
for(int b=a+1;b<length;b++)
{
int j = dataSet[a];
int k = dataSet[b];

// pr¾fen ob gemeinsamer Teiler vorhanden
if(ggT(j,k)==1) noGTcount++;
}
}

// Pi berechnen wenn Paare ohne gemeinsamen Teiler vorhanden
if(noGTcount!=0)
{
double Pi = Math.sqrt((((double)numberOfPairs) / ((double)noGTcount)) * 6.0);
System.out.printf("%.7g\n",Pi);
}
else
{
System.out.println("No estimate for this data set.");
}

}

}

private static int ggT(int a, int b)
{
if(b==0) return a;
return ggT(b,a%b);
}


}