import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.stream.Stream;

public class Main {

	public static void main(String[] args) throws IOException {

		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		// L K
		int[] lk = Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
		int numL = lk[0];
		int numK = lk[1];

		int count = 0;

		while (numL > numK * 2 * count) {
			count++;
		}

		System.out.println(numK * (count - 1));

	}

}