#include #include using namespace std; #define ll long long #define mod 100000007 #define rep(i, n) for (int i = 0; i < n; ++i) using Graph = vector>; 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; }