#include <bits/stdc++.h>
#include <string.h>
#define rep(i,n) for(int i = 0; i < n; i++)
#define srep(i,a,b) for(int i = a; i < b; i++)
#define all(A) (A).begin(),A.end()
#define MOD 1000000007
using namespace std;
using ll = long long;
using P = pair<char,int>;
using Graph = vector<vector<int>>;

int main(void){
	int n,k; cin >> n >> k;
	cout << fixed << setprecision(10) << 1.0/((n+1)*k)*k*(0.5*n*(n+1));
}