#include <bits/stdc++.h>
using namespace std;
int main(){
	long long l,k,ans=0;
	cin>>l>>k;
	ans=l/(k*2);
	if(ans==0) cout<<ans*k<<endl;
	else if(l%ans!=0) cout<<ans*k<<endl;
	else cout<<(ans-1)*k<<endl;
	return 0;
}