source_code: 
  import java.util.*;
  import java.lang.*;
  import java.io.*;
  
  public class  ER23C {
      static long s;
      public static void main (String[] args) throws java.lang.Exception {
          InputReader in = new InputReader(System.in);
          PrintWriter w = new PrintWriter(System.out);
          long n = in.nextLong();
          s = in.nextLong();
          long l = 0, h = n;
          while (l < h) {
              long mid = (l + h ) / 2;
             // System.out.println("mid is : " + mid);
             // System.out.println("high is : " + h);
              //System.out.println("low is : " + l);
              if (Ok(mid))
                  h = mid;
              else
                  l = mid + 1;
          }
          if (Ok(h))
              w.println(n - h + 1);
          else
              w.println(n - h);
  
          w.close();
  
      }
      static boolean Ok(long n) {
          int sum = 0;
          long temp = n;
          while (n > 0) {
              sum += (n % 10);
              n = n / 10;
          }
          //System.out.println("n is :" + n + " sum is : " + sum);
          return (temp - sum >= s);
      }
      static class InputReader {
          private InputStream stream;
          private byte[] buf = new byte[1024];
          private int curChar;
          private int numChars;
  
          public InputReader(InputStream stream) {
              this.stream = stream;
          }
  
          public int read() {
              if (numChars == -1)
                  throw new UnknownError();
              if (curChar >= numChars) {
                  curChar = 0;
                  try {
                      numChars = stream.read(buf);
                  } catch (IOException e) {
                      throw new UnknownError();
                  }
                  if (numChars <= 0)
                      return -1;
              }
              return buf[curChar++];
          }
  
          public int peek() {
              if (numChars == -1)
                  return -1;
              if (curChar >= numChars) {
                  curChar = 0;
                  try {
                      numChars = stream.read(buf);
                  } catch (IOException e) {
                      return -1;
                  }
                  if (numChars <= 0)
                      return -1;
              }
              return buf[curChar];
          }
  
          public void skip(int x) {
              while (x-- > 0)
                  read();
          }
  
          public int nextInt() {
              return Integer.parseInt(next());
          }
  
          public long nextLong() {
              return Long.parseLong(next());
          }
  
          public String nextString() {
              return next();
          }
  
          public String next() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              StringBuffer res = new StringBuffer();
              do {
                  res.appendCodePoint(c);
                  c = read();
              } while (!isSpaceChar(c));
  
              return res.toString();
          }
  
          public String nextLine() {
              StringBuffer buf = new StringBuffer();
              int c = read();
              while (c != '\n' && c != -1) {
                  if (c != '\r')
                      buf.appendCodePoint(c);
                  c = read();
              }
              return buf.toString();
          }
  
          public double nextDouble() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = read();
              }
              double res = 0;
              while (!isSpaceChar(c) && c != '.') {
                  if (c == 'e' || c == 'E')
                      return res * Math.pow(10, nextInt());
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = read();
              }
              if (c == '.') {
                  c = read();
                  double m = 1;
                  while (!isSpaceChar(c)) {
                      if (c == 'e' || c == 'E')
                          return res * Math.pow(10, nextInt());
                      if (c < '0' || c > '9')
                          throw new InputMismatchException();
                      m /= 10;
                      res += (c - '0') * m;
                      c = read();
                  }
              }
              return res * sgn;
          }
          public int[] nextIntArray(int n) {
              int[] a = new int[n];
              for (int i = 0; i < n; i++)
                  a[i] = nextInt();
              return a;
          }
          public long[] nextLongArray(int n) {
              long[] a = new long[n];
              for (int i = 0; i < n; i++)
                  a[i] = nextLong();
              return a;
          }
          public boolean hasNext() {
              int value;
              while (isSpaceChar(value = peek()) && value != -1)
                  read();
              return value != -1;
          }
  
          private boolean isSpaceChar(int c) {
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
  
      }
  }
  