import java.util.*;
public class Main {
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        long N = sc.nextLong();
        long K = sc.nextLong();
        long ans = 0;
        if(N <= K/2){
            ans = N;
        }else if(N < K){
            ans = K-N;
        }else{
            N = N%K;
            if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            }
        }
        System.out.println(ans);
    }

} import java.util.*; util.* java public class Main {
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        long N = sc.nextLong();
        long K = sc.nextLong();
        long ans = 0;
        if(N <= K/2){
            ans = N;
        }else if(N < K){
            ans = K-N;
        }else{
            N = N%K;
            if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            }
        }
        System.out.println(ans);
    }

} Main public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        long N = sc.nextLong();
        long K = sc.nextLong();
        long ans = 0;
        if(N <= K/2){
            ans = N;
        }else if(N < K){
            ans = K-N;
        }else{
            N = N%K;
            if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            }
        }
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        long N = sc.nextLong();
        long K = sc.nextLong();
        long ans = 0;
        if(N <= K/2){
            ans = N;
        }else if(N < K){
            ans = K-N;
        }else{
            N = N%K;
            if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            }
        }
        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) long N = sc.nextLong(); N sc.nextLong() sc.nextLong sc long K = sc.nextLong(); K sc.nextLong() sc.nextLong sc long ans = 0; ans 0 if(N <= K/2){
            ans = N;
        }else if(N < K){
            ans = K-N;
        }else{
            N = N%K;
            if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            }
        } N <= K/2 N K/2 K 2 {
            ans = N;
        } ans = N ans N if(N < K){
            ans = K-N;
        }else{
            N = N%K;
            if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            }
        } N < K N K {
            ans = K-N;
        } ans = K-N ans K-N K N {
            N = N%K;
            if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            }
        } N = N%K N N%K N K if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            } N<=K/2 N K/2 K 2 {
                ans = N;
            } ans = N ans N {
                ans = K-N;
            } ans = K-N ans K-N K N System.out.println(ans) System.out.println System.out System System.out ans String args[] args public class Main {
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        long N = sc.nextLong();
        long K = sc.nextLong();
        long ans = 0;
        if(N <= K/2){
            ans = N;
        }else if(N < K){
            ans = K-N;
        }else{
            N = N%K;
            if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            }
        }
        System.out.println(ans);
    }

} public class Main {
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        long N = sc.nextLong();
        long K = sc.nextLong();
        long ans = 0;
        if(N <= K/2){
            ans = N;
        }else if(N < K){
            ans = K-N;
        }else{
            N = N%K;
            if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            }
        }
        System.out.println(ans);
    }

} Main
import java.util.*;
public class Main {
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        long N = sc.nextLong();
        long K = sc.nextLong();
        long ans = 0;
        if(N <= K/2){
            ans = N;
        }else if(N < K){
            ans = K-N;
        }else{
            N = N%K;
            if(N<=K/2){
                ans = N;
            }else{
                ans = K-N;
            }
        }
        System.out.println(ans);
    }

}
