source_code: import java.io.OutputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.PrintWriter;
  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
   */
  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 {
          int digitsum(long n) {
              int ans = 0;
              while (n > 0) {
                  ans += n % 10;
                  n /= 10;
              }
              return ans;
          }
  
          public void solve(int testNumber, InputReader in, PrintWriter out) {
              long n = in.nextLong();
              long s = in.nextLong();
  
              if (s >= n) {
                  out.println(0);
                  return;
              }
  
              long ans = s;
              while (ans < s + digitsum(ans)) {
                  ans++;
              }
  
              if (n >= ans) {
                  out.println(n - ans + 1);
              } else {
                  out.println(0);
              }
  
  
          }
  
      }
  
      static class InputReader {
          public BufferedReader reader;
          public StringTokenizer tokenizer;
  
          public InputReader(InputStream stream) {
              reader = new BufferedReader(new InputStreamReader(stream), 32768);
              tokenizer = null;
          }
  
          public String next() {
              while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                  try {
                      tokenizer = new StringTokenizer(reader.readLine());
                  } catch (IOException e) {
                      throw new RuntimeException(e);
                  }
              }
              return tokenizer.nextToken();
          }
  
          public long nextLong() {
              return Long.parseLong(next());
          }
  
      }
  }
  
  