import java.util.Scanner;

public class Main {

	public static Scanner in = new Scanner(System.in);

	public static void main(String[] args) {
		int n = in.nextInt(), k = in.nextInt();
		long ans = 0;
		for (int i = 1; i <= n - 1; i++) {
			ans = Math.max(ans, i / k + i % k);
		}
		System.out.println(ans);
	}
}