import java.util.*;
public class Main {
        static Scanner sc = new Scanner(System.in);
        static void myout(Object t){System.out.println(t);}//standard output
        static void myerr(Object t){System.err.println(t);}//standard error
        static String getStr(){return sc.next();}
        static int getInt(){return Integer.parseInt(getStr());}
        static long getLong(){return Long.parseLong(getStr());}
        static boolean hasNext(){return sc.hasNext();}
        static char[] mySplit(String str){return str.toCharArray();}
        public static void main(String[] args){
          long N = getLong();
          long K = getLong();
          
          N %= K;
          if(N > K / 2){
            N = K % N;
          }
          myout(N);
        }
        //Method addition frame start

        //Method addition frame end
}

/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