import java.util.Scanner;
class pokkii{
	public static void main(String args[]){
		Scanner s = new Scanner(System.in);
		int L = s.nextInt();
		int K = s.nextInt();
		int i = 0;
		int sum = 0;
		while(K * 2 * i < L){
			i++;
			sum += K * 2;
		}
		if(sum >= L){
			System.out.println(K * (i - 1));
		}else{
			System.out.println(K * i);
		}
	}
}