#include <bits/stdc++.h>
#include <numeric>
using namespace std;
#define ll long long
#define mod 100000007
#define rep(i, n) for (int i = 0; i < n; ++i)
using Graph = vector<vector<int>>;
ll lcm(ll a, ll b)
{
    return a * b / __gcd(a, b);
}

int main()
{
    cin.tie(0);
    int N, K;
    cin >> N >> K;
    double ans = 0.0;
    ll bunbo = (N + 1) * K;
    for (int i = 0; i < N + 1; i++)
    {
        ans += i * K;
    }
    cout << (double)ans / bunbo << endl;
}