// Problem: 817_C. Really Big Numbers
// Time complexity: logn
import java.util.*;

import javax.swing.Painter;

import java.io.*;

public class C {
	FastScanner in;
	PrintWriter out;
	boolean systemIO = true;
	
	public static class Pair implements Comparable<Pair> {
		int x;
		int y;
		public Pair(int x, int y) {
			super();
			this.x = x;
			this.y = y;
		}
		@Override
		public int compareTo(Pair o) {
			return x - o.x;
		}
		
	}
	
	public static void quickSort(long[] a, int from, int to) {
		if (to - from <= 1) {
			return;
		}
		int i = from;
		int j = to - 1;
		long x = a[from + (new Random()).nextInt(to - from)];
		while (i <= j) {
			while (a[i] < x) {
				i++;
			}
			while (a[j] > x) {
				j--;
			}
			if (i <= j) {
				long t = a[i];
				a[i] = a[j];
				a[j] = t;
				i++;
				j--;
			}
		}
		quickSort(a, from, j + 1);
		quickSort(a, j + 1, to);
	}
	
	public static long check(long x) {
		long sum = 0;
		long k = x;
		while (x > 0) {
			sum += x % 10;
			x /= 10;
		}
		return k - sum;
	}
	
	public void solve() throws IOException {
		long n = in.nextLong();
		long s = in.nextLong();
		long ans = 0;
		for (long i = s; i <= Math.min(n, s + 10000L); i++) {
			if (check(i) >= s) {
				ans++;
			}
		}
		ans += (n - Math.min(n, s + 10000L));
		System.out.println(ans);
	}

	public void run() throws IOException {
		if (systemIO) {
			in = new FastScanner(System.in);
			out = new PrintWriter(System.out);
		} else {
			in = new FastScanner(new File("input.txt"));
			out = new PrintWriter(new File("output.txt"));
		}
		solve();

		out.close();
	}

	class FastScanner {
		BufferedReader br;
		StringTokenizer st;

		FastScanner(File f) {
			try {
				br = new BufferedReader(new FileReader(f));
			} catch (FileNotFoundException e) {
				e.printStackTrace();
			}
		}

		FastScanner(InputStream f) {
			br = new BufferedReader(new InputStreamReader(f));
		}

		String nextLine() {
			try {
				return br.readLine();
			} catch (IOException e) {
				return null;
			}
		}

		String next() {
			while (st == null || !st.hasMoreTokens()) {
				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());
		}

	}

	// AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
	public static void main(String[] arg) throws IOException {
		new C().run();
	}
}