import java.util.*;
public class Main{
  
  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    Long N=scanner.nextLong();
    Long K=scanner.nextLong();
    

    if (K==1){
        System.out.println(0);
    }else if(K>N*2){
        System.out.println(N);
    }else{
        N=(N>K)?N%K:K%N;
        do{
            N=Math.abs(N-K);
        }while(N>Math.abs(N-K));
        /*while(N>Math.abs(N-K)){
            N=Math.abs(N-K);
            
        }*/
        System.out.println(N);
    }
  }

}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz