#include<iostream>
#include<iomanip>
#include<cmath>
#include<string>
#include<algorithm>
#include<vector>
#include<math.h>
#include<stack>
using namespace std;
int main(void){
    long L, K; cin >> L >> K;
    long leng; int cnt = 0;
    if(L % 2 != 0) {
        leng = (L+1) / 2;
        while(true){
        if(leng < K) break;
        leng -= K;    
        cnt++;
        }
        if(L % K != 0){
        cout << (cnt - 1) * K << endl;
        }else{
            cout << cnt * K << endl;
        }
    
    }else{
        leng = L/2;
    while(true){    
        if(leng < K) break;
        leng -= K;    
        cnt++;
    }
    cout << cnt * K << endl;
    }
    return 0;
}