import java.util.Scanner;

public class PokkyGame {

    public static void main(String[] args) {
        
        Scanner scanner = new Scanner(System.in);
        
        int l = scanner.nextInt();
        int k = scanner.nextInt();
        
        //一回で減る長さ
        int eat = k * 2;
        
        int count = 0;
        
        while((l -= eat) > 0){
            
            count++;
            
            
        }
        
        System.out.println(count * k);
        
    }
}