UVa 412 - Pi

// UVa 412 - Pi

#include <iostream>
#include <stdio.h>
#include <math.h>

using namespace std;

int gcd(int a, int b) {
	if (a < b)
		return gcd(b, a);
	if (b == 0)
		return a;
	else
		return gcd(b, a % b);
}

int main() {

	int n, a[51];
	cin >> n;
	while (n) {

		int c = 0;
		for (int i = 0; i < n; i++) {
			cin >> a[i];
			for (int j = 0; j < i; j++) {
				int g = gcd(a[i], a[j]);
				if (g == 1)
					c++;
			}
		}

		if (c == 0)
			cout << "No estimate for this data set." << endl;
		else {
			double s = sqrt(6.0 * n * (n - 1) / 2 / c);
			printf("%.6f\n", s);
		}

		cin >> n;
	}

}