source_code: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.util.StringTokenizer;
  import java.util.Arrays;
  import java.util.ArrayList;
  
  public class C{
  	
  	static long s;
  	public static void main(String[] args)throws IOException {
  		Reader.init(System.in);
  		long n=Reader.nextLong();
  		s=Reader.nextLong();
  		long lo=1,hi=n,mid;
  		while(lo<hi){
  			mid=(lo+hi)/2;
  			if(diff(mid)>=s)
  				hi=mid;
  			else
  				lo=mid+1;
  		}
  		if(diff(lo)>=s)
  			System.out.println(n-lo+1);
  		else
  			System.out.println(0);
  	}
  	
  	static long diff(long n){
  		String s=String.valueOf(n);
  		int sum=0;
  		
  		for(int i=0;i<s.length();i++){
  			
  			sum+=Integer.parseInt(s.valueOf(s.charAt(i)));
  		}
  		return (n-sum);
  	}
  		
  		
  }
  
  
  		
  /** Class for buffered reading int and double values */
  class Reader {
      static BufferedReader reader;
      static StringTokenizer tokenizer;
  
      /** call this method to initialize reader for InputStream */
      static void init(InputStream input) {
          reader = new BufferedReader(
                       new InputStreamReader(input) );
          tokenizer = new StringTokenizer("");
      }
  
      /** get next word */
      static String next() throws IOException {
          while ( ! tokenizer.hasMoreTokens() ) {
              //TODO add check for eof if necessary
              tokenizer = new StringTokenizer(
                     reader.readLine() );
          }
          return tokenizer.nextToken();
      }
  
      static int nextInt() throws IOException {
          return Integer.parseInt( next() );
      }
      
      static long nextLong() throws IOException {
          return Long.parseLong( next() );
      }
  	
      static double nextDouble() throws IOException {
          return Double.parseDouble( next() );
      }
  }