//Normal

#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

void print(auto a){
  cout << a;
}

void prints(auto a){
  cout << a << " ";
}

void prints(){
  cout << " ";
}

void printl(auto a){
  cout << a << endl;
}

void printl(){
  cout << endl;
}

void fix(int n){
  cout << fixed << setprecision(n);
}

int siz(string s){
  return (int)s.size();
}

int main(){
  ll L, K; cin >> L >> K;
  int ok = 0, ng = 1e9;
  while(ok+1 < ng){
    int mid = (ok+ng)/2;
    
    0 < L-mid*K*2 ? ok = mid : ng = mid;
  }
  
  printl(ok*K);
  return 0;
}