#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; #define endl '\n' #define all(v) (v).begin(), (v).end() #define rall(v) (v).rbegin(), (v).rend() #define uniq(v) (v).erase(unique((v).begin(), (v).end()), (v).end()) typedef long long ll; typedef long double lb; typedef pair P; typedef complex comp; typedef vector< vector > matrix; struct pairhash { public: template size_t operator()(const pair &x) const { size_t seed = hash()(x.first); return hash()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2); } }; const int inf = 1e9 + 9; const ll mod = 1e9 + 7; const double eps = 1e-8; const double pi = acos(-1); int l, k; int solve() { return ((l / (2*k)) - (l%(2*k)==0)) * k; } void input() { cin >> l >> k; } int main() { ios::sync_with_stdio(false); cin.tie(0); cout << fixed << setprecision(15); input(); cout << solve() << endl; }