//
//  main.cpp
//  AndeyLess
//
//  Created by Kadir Kadyrov on 08.07.2020.
//  Copyright © 2020 Kadir Kadyrov. All rights reserved.
//

#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>

using namespace std;

int main() {
    int n;
    double x;
    cin >> n >> x;
    double sum = 0;
    for (int i = 1; i <= n; i++) {
        sum += (pow(x, i - 1) / (i * i - 2));
    }

    cout << sum << endl;

}