#include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; #define REP(i,a,n) for(int i=(a); i<(int)(n); i++) #define rep(i,n) REP(i,0,n) #define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it) #define ALLOF(c) (c).begin(), (c).end() typedef long long ll; int main(){ int L, K; cin >> L >> K; int R = L/2 + (L%2!=0); if(R <= K){ cout << 0 << endl; } else{ cout << K * ((R/K) - (R%K==0)) << endl; } return 0; }