#include <algorithm>
#include <numeric>
#include <string>
#include <vector>
#include <iostream>
#include <queue>
#include <utility>
#include <cmath>
using namespace std;

using ull = unsigned long long;

int main()
{
    ull l,k;
    cin >> l >> k;

    int num = ceil(l/(2*k));

    if(num & 1)
        cout << (num-1)*k << endl;
    else
        cout << num*k << endl;
}