#include using namespace std; #ifdef DEBUG_ #include #else #define dump(...) #endif #define FastIO cin.tie(nullptr), ios_base::sync_with_stdio(false); #define rep(i, n) for (int i = 0; i < (int)(n); ++i) #define out(msg) cout << (msg) << '\n' #define die(msg) \ do { \ cout << msg << endl; \ exit(0); \ } while (0) #define all(k) k.begin(), k.end() #define rall(k) k.rbegin(), k.rend() #define INFi 1 << 30 #define INFll 1LL << 60 template bool chmax(T& a, const T& b) { return ((a < b) ? (a = b, true) : (false)); } template bool chmin(T& a, const T& b) { return ((a > b) ? (a = b, true) : false); } using llint = long long int; int main() { FastIO; long double N, K; cin >> N >> K; long double dice = (N + 1) * K; long double ans{}; for (long double n = 0; n < N + 1; ++n) { ans += n * K; } cout << fixed << setprecision(5); out(ans / dice); }