source_code: import java.io.OutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PrintWriter;
  import java.util.Scanner;
  
  /**
   * Built using CHelper plug-in
   * Actual solution is at the top
   */
  public class Main {
      public static void main(String[] args) {
          InputStream inputStream = System.in;
          OutputStream outputStream = System.out;
          Scanner in = new Scanner(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, Scanner in, PrintWriter out) {
              long n = in.nextLong();
              long s = in.nextLong();
              long ans = 0;
              long i = 0;
              for (i = s; i <= n; i++) {
                  long t = i - sum(i);
                  if (t >= s) {
                      if (i % 10 == 9) {
                          break;
                      }
                      ans++;
                  }
              }
              if (n >= s) {
                  out.println(ans - i + n + 1);
              } else {
                  out.println(0);
              }
          }
  
          static long sum(long a) {
              long sum = 0;
              while (a != 0) {
                  sum += (a % 10);
                  a /= 10;
              }
              return sum;
          }
  
      }
  }
  
  