source_code: import java.io.*;
  import java.util.*;
  
  public class Main {
      public static void main(String[] args) throws IOException {
          InputStream inputStream = System.in;
  //        InputStream inputStream = new FileInputStream("dijkstra.in");
          OutputStream outputStream = System.out;
  //        OutputStream outputStream = new FileOutputStream("dijkstra.out");
          InputReader in = new InputReader(inputStream);
          PrintWriter out = new PrintWriter(outputStream);
          Answer solver = new Answer();
          solver.solve(in, out);
          out.close();
      }
  }
  
  class Answer {
      private int sumd(long x) {
          int sum = 0;
          while (x != 0) {
              sum += x % 10;
              x /= 10;
          }
          return sum;
      }
  
      private long bin(long l, long r, long s) {
          if (l > r) {
              return -1;
          }
          long x = (l + r) >> 1;
          int sum = sumd(x);
          if (x - sum < s) {
              return bin(x + 1, r, s);
          }
          long t = bin(l, x - 1, s);
          if (t != -1) {
              return t;
          }
          return x;
      }
  
      public void solve(InputReader in, PrintWriter out) throws IOException {
          long n = in.nextLong();
          long s = in.nextLong();
          long t = bin(1, n, s);
          if (t == -1) {
              out.print("0");
          } else {
              long ans = n - t + 1;
              out.print(ans);
          }
      }
  }
  
  class InputReader {
      private BufferedReader reader;
      private StringTokenizer tokenizer;
  
      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 int nextInt() {
          return Integer.parseInt(next());
      }
  
      public long nextLong() {
          return Long.parseLong(next());
      }
  }
  