

import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class Main {

	public static void main(String args[]) throws Exception {
		MyScanner sc = new MyScanner();
		out = new PrintWriter(new BufferedOutputStream(System.out));
		
		long n = sc.nextLong();
		long k = sc.nextLong();
		long min = n;
		if(k == 1) {
			System.out.println("0");
			return;
		}
		if(n % k == 0) {
			System.out.println("0");
			return;
		}
		if(n > k) {
			long divisor = n / k;
			long rem = n - (divisor * k);
			n = rem;
		}
		min = n;
		while(Math.abs(n - k) <= min) {
			n = Math.abs(n - k);
			min = Math.min(min, n);
		}
		System.out.println(n);
	}

	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}

} import java.io.BufferedOutputStream; BufferedOutputStream java.io import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.PrintWriter; PrintWriter java.io import java.util.StringTokenizer; StringTokenizer java.util public class Main {

	public static void main(String args[]) throws Exception {
		MyScanner sc = new MyScanner();
		out = new PrintWriter(new BufferedOutputStream(System.out));
		
		long n = sc.nextLong();
		long k = sc.nextLong();
		long min = n;
		if(k == 1) {
			System.out.println("0");
			return;
		}
		if(n % k == 0) {
			System.out.println("0");
			return;
		}
		if(n > k) {
			long divisor = n / k;
			long rem = n - (divisor * k);
			n = rem;
		}
		min = n;
		while(Math.abs(n - k) <= min) {
			n = Math.abs(n - k);
			min = Math.min(min, n);
		}
		System.out.println(n);
	}

	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}

} Main public static PrintWriter out; out public static void main(String args[]) throws Exception {
		MyScanner sc = new MyScanner();
		out = new PrintWriter(new BufferedOutputStream(System.out));
		
		long n = sc.nextLong();
		long k = sc.nextLong();
		long min = n;
		if(k == 1) {
			System.out.println("0");
			return;
		}
		if(n % k == 0) {
			System.out.println("0");
			return;
		}
		if(n > k) {
			long divisor = n / k;
			long rem = n - (divisor * k);
			n = rem;
		}
		min = n;
		while(Math.abs(n - k) <= min) {
			n = Math.abs(n - k);
			min = Math.min(min, n);
		}
		System.out.println(n);
	} main {
		MyScanner sc = new MyScanner();
		out = new PrintWriter(new BufferedOutputStream(System.out));
		
		long n = sc.nextLong();
		long k = sc.nextLong();
		long min = n;
		if(k == 1) {
			System.out.println("0");
			return;
		}
		if(n % k == 0) {
			System.out.println("0");
			return;
		}
		if(n > k) {
			long divisor = n / k;
			long rem = n - (divisor * k);
			n = rem;
		}
		min = n;
		while(Math.abs(n - k) <= min) {
			n = Math.abs(n - k);
			min = Math.min(min, n);
		}
		System.out.println(n);
	} MyScanner sc = new MyScanner(); sc new MyScanner() out = new PrintWriter(new BufferedOutputStream(System.out)) out new PrintWriter(new BufferedOutputStream(System.out)) long n = sc.nextLong(); n sc.nextLong() sc.nextLong sc long k = sc.nextLong(); k sc.nextLong() sc.nextLong sc long min = n; min n if(k == 1) {
			System.out.println("0");
			return;
		} k == 1 k 1 {
			System.out.println("0");
			return;
		} System.out.println("0") System.out.println System.out System System.out "0" return; if(n % k == 0) {
			System.out.println("0");
			return;
		} n % k == 0 n % k n k 0 {
			System.out.println("0");
			return;
		} System.out.println("0") System.out.println System.out System System.out "0" return; if(n > k) {
			long divisor = n / k;
			long rem = n - (divisor * k);
			n = rem;
		} n > k n k {
			long divisor = n / k;
			long rem = n - (divisor * k);
			n = rem;
		} long divisor = n / k; divisor n / k n k long rem = n - (divisor * k); rem n - (divisor * k) n (divisor * k) divisor k n = rem n rem min = n min n while(Math.abs(n - k) <= min) {
			n = Math.abs(n - k);
			min = Math.min(min, n);
		} Math.abs(n - k) <= min Math.abs(n - k) Math.abs Math n - k n k min {
			n = Math.abs(n - k);
			min = Math.min(min, n);
		} n = Math.abs(n - k) n Math.abs(n - k) Math.abs Math n - k n k min = Math.min(min, n) min Math.min(min, n) Math.min Math min n System.out.println(n) System.out.println System.out System System.out n String args[] args public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	} MyScanner BufferedReader br; br StringTokenizer st; st public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		} MyScanner {
			br = new BufferedReader(new InputStreamReader(System.in));
		} br = new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		} next {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		} while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			} st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			} try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				} catch (IOException e) {
					e.printStackTrace();
				} IOException e {
					e.printStackTrace();
				} e.printStackTrace() e.printStackTrace e {
					st = new StringTokenizer(br.readLine());
				} st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() {
			return Integer.parseInt(next());
		} nextInt {
			return Integer.parseInt(next());
		} return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() {
			return Long.parseLong(next());
		} nextLong {
			return Long.parseLong(next());
		} return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nextDouble() {
			return Double.parseDouble(next());
		} nextDouble {
			return Double.parseDouble(next());
		} return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		} nextLine {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		} String str = ""; str "" try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			} catch (IOException e) {
				e.printStackTrace();
			} IOException e {
				e.printStackTrace();
			} e.printStackTrace() e.printStackTrace e {
				str = br.readLine();
			} str = br.readLine() str br.readLine() br.readLine br return str; str public class Main {

	public static void main(String args[]) throws Exception {
		MyScanner sc = new MyScanner();
		out = new PrintWriter(new BufferedOutputStream(System.out));
		
		long n = sc.nextLong();
		long k = sc.nextLong();
		long min = n;
		if(k == 1) {
			System.out.println("0");
			return;
		}
		if(n % k == 0) {
			System.out.println("0");
			return;
		}
		if(n > k) {
			long divisor = n / k;
			long rem = n - (divisor * k);
			n = rem;
		}
		min = n;
		while(Math.abs(n - k) <= min) {
			n = Math.abs(n - k);
			min = Math.min(min, n);
		}
		System.out.println(n);
	}

	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}

} public class Main {

	public static void main(String args[]) throws Exception {
		MyScanner sc = new MyScanner();
		out = new PrintWriter(new BufferedOutputStream(System.out));
		
		long n = sc.nextLong();
		long k = sc.nextLong();
		long min = n;
		if(k == 1) {
			System.out.println("0");
			return;
		}
		if(n % k == 0) {
			System.out.println("0");
			return;
		}
		if(n > k) {
			long divisor = n / k;
			long rem = n - (divisor * k);
			n = rem;
		}
		min = n;
		while(Math.abs(n - k) <= min) {
			n = Math.abs(n - k);
			min = Math.min(min, n);
		}
		System.out.println(n);
	}

	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}

} Main


import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class Main {

	public static void main(String args[]) throws Exception {
		MyScanner sc = new MyScanner();
		out = new PrintWriter(new BufferedOutputStream(System.out));
		
		long n = sc.nextLong();
		long k = sc.nextLong();
		long min = n;
		if(k == 1) {
			System.out.println("0");
			return;
		}
		if(n % k == 0) {
			System.out.println("0");
			return;
		}
		if(n > k) {
			long divisor = n / k;
			long rem = n - (divisor * k);
			n = rem;
		}
		min = n;
		while(Math.abs(n - k) <= min) {
			n = Math.abs(n - k);
			min = Math.min(min, n);
		}
		System.out.println(n);
	}

	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}

}
