source_code: import java.math.BigInteger;
  import java.util.*;
  public class C {
      
      public static void main(String[] args)
      {
          Scanner sc = new Scanner(System.in);
          long n = sc.nextLong();
          long s = sc.nextLong();
          
          BigInteger k = findFirst(BigInteger.valueOf(s));
          if (BigInteger.valueOf(n).compareTo(k) >= 0)
          {
              System.out.println(n - k.longValue() + 1);
          }
          else
          {
              System.out.println("0");
          }
      }
      
      public static BigInteger findFirst(BigInteger s) // first number where sum of digs >= s
      {
          BigInteger b = BigInteger.ZERO;
          while (cd(b).compareTo(b.subtract(s)) > 0)
          {
              BigInteger c = BigInteger.ONE;
              while (cd(b.add(c)).compareTo(b.add(c).subtract(s)) > 0) {
                  c = c.multiply(BigInteger.TEN);
              }
              // possibly overshot
              c = c.divide(BigInteger.TEN);
              if (c.compareTo(BigInteger.TEN) < 0) c = BigInteger.TEN; // always add at least 10
              b = b.add(c);
          }
          return b;
      }
      
      public static BigInteger cd(BigInteger n)
      {
          BigInteger t = BigInteger.ZERO;
          while (n.compareTo(BigInteger.ZERO) > 0)
          {
              t = t.add(n.mod(BigInteger.TEN));
              n = n.divide(BigInteger.TEN);
          }
          return t;
      }
  }
  