source_code: import java.io.*;
  import java.util.*;
  
  
  public class Main {
  
  	class IO {
  		BufferedReader reader;
  		PrintWriter writer;
  		StringTokenizer tokenizer;
  
  		IO() {
  			reader = new BufferedReader(new InputStreamReader(System.in));
  			writer = new PrintWriter(new BufferedOutputStream(System.out));
  			tokenizer = new StringTokenizer("");
  		}
  
  		IO(String file) throws FileNotFoundException {
  			reader = new BufferedReader(new FileReader(file));
  			writer = new PrintWriter(new BufferedOutputStream(System.out));
  			tokenizer = new StringTokenizer("");
  		}
  
  		String next() throws IOException {
  			while (tokenizer == null || !tokenizer.hasMoreTokens()) {
  				String line = reader.readLine();
  				if (line == null)
  					return null;
  				tokenizer = new StringTokenizer(line);
  			}
  			return tokenizer.nextToken();
  		}
  
  		public Integer nextInt() throws IOException {
  			return Integer.parseInt(next());
  		}
  
  		public Long nextLong() throws IOException {
  			return Long.parseLong(next());
  		}
  
  		public Double nextDouble() throws IOException {
  			return Double.parseDouble(next());
  		}
  
  		public void write(Object obj) {
  			writer.print(obj.toString());
  		}
  
  		public void writeSpace(Object obj) {
  			writer.print(obj.toString() + " ");
  		}
  
  		public void writeLine(Object obj) {
  			writer.println(obj.toString());
  		}
  
  		public void close() {
  			writer.close();
  		}
  	}
  
  	IO io;
  
  	Main() {
  		io = new IO();
  	}
  
  	Main(String file) throws FileNotFoundException {
  		io = new IO(file);
  	}
  
  	void solve() throws IOException {
  		long n = io.nextLong(), s = io.nextLong();
  		long min = s;
  		while (true) {
  			min++;
  			long sum = 0, tem = min;
  			while (tem > 0) {
  				sum += tem % 10;
  				tem /= 10;
  			}
  			if (min - sum >= s) break;
  		}
  		io.write(Math.max(0, n - min + 1));
  	}
  
  	void close() {
  		io.close();
  	}
  
  	public static void main(String args[]) throws IOException {
  		// Main solver = new Main("input.txt");
  		Main solver = new Main();
  		solver.solve();
  		solver.close();
  	}
  }
  