#include<stdio.h>

void run(void){
  int N,K;
  scanf("%d%d",&N,&K);
  if(N==K){
    printf("1\n");
    return;
  }
  if(K==1){
    if(N==2){
      printf("0\n");
    } else {
      printf("%d\n",(1<<(N-1))-N+1);
    }
  } else {
    printf("%d\n",(1<<(N-K)));
  }
  return;
}

int main(void){
  run();
  return 0;
}