import java.io.*;
class no63
{
    public static void main(String args[])throws IOException
    {
	BufferedReader sc=new BufferedReader(new InputStreamReader(System.in));
	String lk[]=sc.readLine().split(" ");
	int l,k,ans=0;
	l=Integer.parseInt(lk[0]);
	k=Integer.parseInt(lk[1]);
        while(l>0)
	    {
		l-=2*k;
		if(l<=0)break;
		ans++;
	    }
	System.out.println(ans*k);
    }
}