#include <vector>
#include <algorithm>
#include <iomanip>
#include <math.h>
#include <fstream>

using namespace std;

double bin_search(double begin, double end, int n, double a)
{
	double middle = begin + (end - begin) / 2;
	vector <double> arr = { a, middle };
	for (int i = 2; i < n; ++i)
		arr.push_back(2 * (1 + arr.at(i - 1)) - arr.at(i - 2));

	if (end - begin > 0.000000000001)
		if (*min_element(arr.begin(), arr.end()) >= 0)
			return bin_search(begin, middle, n, a);
		else
			return bin_search(middle, end, n, a);

	return arr.at(arr.size() - 1);
}
int main()
{
	ifstream ist("garland.in");
	ofstream ost("garland.out");

	int n;			// [3 : 1000]
	double A;		// [10 : 1000.0]
	ist >> n >> A;

	double B = abs(bin_search(0, 1000, n, A));
	ost << fixed << setprecision(2) << B;

	return 0;
}