#include <bits/stdc++.h>
#define INF 990000000
//5
using namespace std;


int main() {
int s,t;
cin>>s;
cin>>t;
int count=0;
while(true){
count++;
s-=(t*2);
if(s<=0){
break;
}
}
cout <<(t)*(count-1)<<endl;



}