#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <math.h>
using namespace std;
int n;
double z;
double z2;
double a;
double f (double m)
{
    vector <double> v(1000);
    v[0] = a;
    v[1] = m;
    for (int i = 2; i < n; i++)
        v[i] = 2*(1 + v[i - 1]) - v[i - 2];
    double k;
    for (int i = 0; i < n; i++)
        if (v[i] < k)
            k = v[i];
    return k;
}
double b_res (double m)
{
    vector <double> v(1000);
    v[0] = a;
    v[1] = m;
    for (int i = 2; i < n; i++)
        v[i] = 2*(1 + v[i - 1]) - v[i - 2];
    return v[n-1];
}
double bin_search (double l, double r)
{
    if (r - l > 0.000000000001)
    {
        double m = (l + r) / 2;
        z = b_res(m);
        z2 = f(m);
        if (z2 >= 0)
            bin_search(l, m);
        else {
            bin_search(m, r);
        }
    }
}
int main() {
    cin >> n >> a;
    double l = 0;
    double r = 1000;
    bin_search(l, r);
    cout << fixed << setprecision(2) << abs(z);
    return 0;
}