#include<stdio.h>

int main()
{
  int l;
  int k;
  int memory = 0;

  scanf("%d %d",&l,&k);


  if(l-2*k>0){
    while(l > 0){//lが正の限りループ
      memory = k;
      l = l-2*k;
      k = k+k;
    }
    printf("%d\n",memory);
  }
  else{
    printf("0\n");
  }
  return 0;
}