#include<stdio.h>
#include<math.h>

void main(){
  int i=0;
  long long int n, k, x[3], xmin;
  scanf("%lld %lld", &n, &k);
  
  x[0] = abs(n-k);
  x[1] = abs(x[0]-k);
  x[2] = abs(x[1]-k);
  while(x[i%3]!=x[(i+2)%3]){
//    printf("%lld %lld %lld\n",x[0],x[1],x[2]);
    x[i%3] = abs(x[(i+2)%3]-k);
    i++;
  }
  xmin = x[0];
  if(xmin>x[1])
    xmin = x[1];
  if(xmin>x[2])
    xmin = x[2];
  
  printf("%lld",xmin);
}