import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int K = sc.nextInt();
    int ans = 0;
    if((K > 0) && (K <= N)) {
      if(K - 1 == N - K) {
        ans = N - 1;
      } else {
        ans = N - 2;
      }
    }
    System.out.println(ans);
  }
}