#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0; i<(n); ++i)
using ll = long long;

int main(){
    int n,k; cin >> n >> k;
    int sum = (n+1)*n/2;
    double ans = 1.0*sum*k / ((n+1) * k);
    cout << setprecision(10) << ans << endl;
}