### Pi

Time Limit: 1000 ms Memory Limit: 10000 KiB

#### Problem Description

Professor Robert A. J. Matthews of the Applied Mathematics and Computer Science department at the University of Aston in Birmingham, England has recently described how the positions of the starts across the night sky may be used to deduce a surprisingly accurate value of pi. This result followed from the application of certain theorems in number theory.

Here, we don't have the night sky, but can use the same theoretical basis to form an estimate for pi.

Given any pair of whole numbers chosen from large, random collection of numbers, the probability that the two numbers hve no common factor other than one (1) is

6/(pi^2)

For example, using the small collection of numbers: 2, 3, 4, 5, 6; there are 10 pairs that can be formed: (2,3), (2,4), etc. Six of the 10 pairs: (2,3), (2,5), (3,4), (3,5), (4,5) and (5,6) have no common factor other that one. Using the ratio of the counts as the probability we have:

6/(pi^2) = 6/10

pi = 3.162

In this problem, you'll receive a series of data sets. Each data set contains a set of pseudo-random positive integers. For each data set, find the portion of the pairs which may be formed tha have no common factor other than one (1), and se the method illustrated above to obtain as estimate for pi. Report this estimate for each data set.

#### Input

The input consists of a series of data sets.

The first line of each data set contains a positive integer value, N, greater than one (1) and less than 50.

There is one positive integer per line for the next N lines that constitute the set for which the pairs are to be examined. These integers are each greater than 0 and less than 32768.

Eachinteger of the input stream has its first digit as the first character on the input line.

The set size desigator, N, will be zero to indicate the end of data.

#### Output

A line with a single real value is to be emitted for each input data set encountered. This value is the estimate for pi for the data set. The default real/float output format should be used. Answers must be within 0.1% of the correct answer.

For some data sets; it may be impossible to estimate a value for pi. This occurs when there are no pairs without common factors. In there cases, emit the single-line message:

No estimate for this data set.

exactly, starting with the first character, "N", as the first character on the line.

#### Sample Input

5
2
3
4
5
6
2
13
39
0

#### Sample Output

3.162
No estimate for this data set.