#include <iostream> 
#include <string> 
#include <vector> 
#include <cmath> 
#include <algorithm> 
#include <cstdlib> 
#include <ctime> 
#include <cstdio> 
#include <functional> 
#include <set> 
#include <sstream> 
#include <cctype>

using namespace std; 


int main(){

	long n,k;
	cin>>n>>k;

	if(n==2*k) cout<<0<<endl;
	else cout<<ceil(n/(2*k))*k<<endl;


	return 0;
}