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

int main(){
	ll n,k; cin>>n>>k;
	n+=1;
	ll b=(n)*k;
	ll ans=0;
	rep(i,n) ans+=i*k;
	cout.precision(10);
	cout << (double)ans/(n*k) << endl;	
}