#include <iostream>
#include <fstream>

using namespace std;


int main(){
    ifstream fin("garland.in");
    ofstream fout("garland.out");
    int n;
    fin >> n;
    double arr[n];
    fin >> arr[0];
    double l = 0, r = arr[0];
    while (r - l > 0.000001){
        arr[1] = (l + r) / 2;
        bool Up = true;
        for (int i = 2; i < n; i++){
            arr[i] = 2 * arr[i - 1] - arr[i - 2] + 2;
            if (arr[i] < 0){
                Up = false;
                break;
            }
        }
        if (Up) r = arr[1];
        else l = arr[1];
    }
    fout.precision(2);
    fout << fixed << arr[n - 1];
    return 0;
}