source_code: import java.util.*;
  import java.io.*;
  
  @SuppressWarnings("Duplicates")
  public class C817 {
      private FastScanner in;
      private PrintWriter out;
  
      private long calcSum(long x) {
          int ans = 0;
          while (x > 0) {
              ans += x % 10;
              x /= 10;
          }
          return ans;
      }
  
      private long calcDiff(long x) {
          return x - calcSum(x);
      }
  
      private long binSearch(long n, long s) {
          long l = 0;
          long r = n + 1;
  
          while (r - l > 1) {
              long m = (r + l) >> 1;
              if (calcDiff(m) >= s) {
                  r = m;
              } else {
                  l = m;
              }
          }
          return l;
      }
  
      private void solve() throws IOException {
          long n = in.nextLong();
          long s = in.nextLong();
  
          long ans = binSearch(n, s);
  
          out.println(n - ans);
      }
  
      private void run() {
          try {
              in = new FastScanner(System.in);
              out = new PrintWriter(System.out);
  
              solve();
  
              out.close();
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
  
      class FastScanner {
          BufferedReader br;
          StringTokenizer st;
  
          FastScanner(InputStream f) {
              br = new BufferedReader(new InputStreamReader(f));
          }
  
          FastScanner(File f) {
              try {
                  br = new BufferedReader(new FileReader(f));
              } catch (FileNotFoundException e) {
                  e.printStackTrace();
              }
          }
  
          String next() {
              while (st == null || !st.hasMoreTokens()) {
                  try {
                      st = new StringTokenizer(br.readLine());
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
              }
              return st.nextToken();
          }
  
          int nextInt() {
              return Integer.parseInt(next());
          }
  
          long nextLong() {
              return Long.parseLong(next());
          }
      }
  
      public static void main(String[] arg) {
          new C817().run();
      }
  }