source_code: 
  import java.io.*;
  import java.util.*;
  
  public class Main {
      public static void main (String[] args) throws java.lang.Exception {
          BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
          StringTokenizer st = new StringTokenizer(br.readLine());
          long n = Long.parseLong(st.nextToken()),
              s = Long.parseLong(st.nextToken());
          long m = s;
          while (m-f(m)<s && m<=n) m++;
          System.out.println(Math.max(n-m+1, 0));
      }
      
      public static int f(long n) {
          int sum = 0;
          for (long i=0, j=1L ; i<(int)Math.log10(n)+1 ; i++, j*=10) {
              sum += (n/j)%10;
          }
          return sum;
      }
      
  }
  
  
  