#include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; #define rep(i, n) for (int i = 0; i < n; i++) #define rep1(i, n) for (int i = 1; i < n + 1; i++) #define all(A) A.begin(), A.end() #define itr(A, l, r) A.begin() + l, A.begin() + r #define debug(var) cout << #var << " = " << var << endl; typedef long long ll; int main(void) { int L, k; cin >> L >> k; L--; cout << L / (2 * k) * k << endl; }