#include <iostream>
#include <vector>
#include <map>
#include<string>
#include<queue>
#include<math.h>
#define all(x) begin(x),end(x)
#define ll long long
#define P pair<int,int>
#define lP pait<ll,ll>
using namespace std;
int main() {
    double n,k,ans=0;
    cin>>n>>k;
    for(int i=0;i<=n;i++){
        ans+=i*k;
    }
    printf("%.1lf\n",ans/((n+1)*k));
    return 0;
}