source_code: import java.io.OutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PrintWriter;
  import java.io.PrintStream;
  import java.util.StringTokenizer;
  import java.io.IOException;
  import java.io.BufferedReader;
  import java.io.InputStreamReader;
  import java.io.InputStream;
  
  /**
   * Built using CHelper plug-in
   * Actual solution is at the top
   *
   * @author Wolfgang Beyer
   */
  public class Main {
      public static void main(String[] args) {
          InputStream inputStream = System.in;
          OutputStream outputStream = System.out;
          InputReader in = new InputReader(inputStream);
          PrintWriter out = new PrintWriter(outputStream);
          TaskC solver = new TaskC();
          solver.solve(1, in, out);
          out.close();
      }
  
      static class TaskC {
          public void solve(int testNumber, InputReader in, PrintWriter out) {
              long n = in.nextLong();
              long s = in.nextLong();
  
              if (n - digitSum(n) < s) {
                  out.println(0);
                  return;
              }
  
              long left = 0;
              long right = n;
              while (left < right) {
                  long mid = left + (right - left) / 2;
                  if (mid - digitSum(mid) >= s) { // if condition(mid) == true
                      right = mid;
                  } else {
                      left = mid + 1;
                  }
              }
              out.println(n - left + 1);
          }
  
          long digitSum(long a) {
              long result = 0;
              while (a > 0) {
                  result += a % 10;
                  a /= 10;
              }
              return result;
          }
  
      }
  
      static class InputReader {
          private static BufferedReader in;
          private static StringTokenizer tok;
  
          public InputReader(InputStream in) {
              this.in = new BufferedReader(new InputStreamReader(in));
          }
  
          public long nextLong() {
              return Long.parseLong(next());
          }
  
          public String next() {
              try {
                  while (tok == null || !tok.hasMoreTokens()) {
                      tok = new StringTokenizer(in.readLine());
                      //tok = new StringTokenizer(in.readLine(), ", \t\n\r\f"); //adds commas as delimeter
                  }
              } catch (IOException ex) {
                  System.err.println("An IOException was caught :" + ex.getMessage());
              }
              return tok.nextToken();
          }
  
      }
  }
  
  