source_code: import java.io.*;
  
  import java.util.*;
  
  public class Solution {
  
      public static void main(String[] args) {
         Scanner scanner = new Scanner(System.in);
  
         long n =   scanner.nextLong();
         long s =   scanner.nextLong();
         long myLong = s;
         long count =0;
        while(true){
      	  if(myLong>n){
      		  break;
      	  }
      	  char[] num = (""+myLong).toCharArray();
  		int sum = 0;
  			for (int j = 0; j < num.length; j++)
  				sum += num[j] - '0';
      	
      	  if(myLong- sum>=s){
      		  //count++;
      		  break;
      	  }
      	  
      	  myLong++;
        }
        System.out.println(Math.max(n-myLong+1,0));
          scanner.close();
      }
  }