import java.io.*; import java.util.*; public class Main_yukicoder415 { public static void main(String[] args) { Scanner sc = new Scanner(System.in); Printer pr = new Printer(System.out); int n = sc.nextInt(); int d = sc.nextInt(); if (n == 1 || n == d) { pr.println(0); } else if (d != 1 && n % d == 0) { pr.println((n - 1) / d); } else { pr.println(n - 1); } pr.close(); sc.close(); } @SuppressWarnings("unused") private static class Scanner { BufferedReader br; Iterator it; Scanner (InputStream in) { br = new BufferedReader(new InputStreamReader(in)); } String next() throws RuntimeException { try { if (it == null || !it.hasNext()) { // it = Arrays.asList(br.readLine().split(" ")).iterator(); it = Arrays.asList(br.readLine().split("\\p{javaWhitespace}+")).iterator(); } return it.next(); } catch (IOException e) { throw new IllegalStateException(); } } int nextInt() throws RuntimeException { return Integer.parseInt(next()); } long nextLong() throws RuntimeException { return Long.parseLong(next()); } float nextFloat() throws RuntimeException { return Float.parseFloat(next()); } double nextDouble() throws RuntimeException { return Double.parseDouble(next()); } void close() { try { br.close(); } catch (IOException e) { // throw new IllegalStateException(); } } } private static class Printer extends PrintWriter { Printer(PrintStream out) { super(out); } } }