source_code: import java.io.*;
  import java.util.*;
  
  public class Main {
  	
  	static InputReader in = new InputReader(System.in);
  	static PrintWriter out = new PrintWriter(System.out);
  	
  	
  	public static void main(String[] args) {
  
  		long n = in.nextLong();
  		long s = in.nextLong();
  		
  		if(diff(n) < s) {
  			System.out.println(0);
  			out.close();
  			return;
  		}
  		
  		long lo = 1;
  		long hi = n;
  		while(lo < hi) {
  			long mid = lo + (hi - lo) / 2;
  			if(diff(mid) >= s)
  				hi = mid;
  			else
  				lo = mid + 1;
  		}
  		System.out.println(n - lo + 1);
  		
  		out.close();
  	}
  
  	static long diff(long n) {
  		char[] ca = (n + "").toCharArray();
  		int sum = 0;
  		for(char c : ca)
  			sum += (c - '0');
  		return n - sum;
  	}
  }
  
  
  class InputReader {
  
  	private final InputStream stream;
  	private final byte[] buf = new byte[8192];
  	private int curChar, snumChars;
  
  	public InputReader(InputStream st) {
  		this.stream = st;
  	}
  
  	public int read() {
  		if (snumChars == -1)
  			throw new InputMismatchException();
  		if (curChar >= snumChars) {
  			curChar = 0;
  			try {
  				snumChars = stream.read(buf);
  			} catch (IOException e) {
  				throw new InputMismatchException();
  			}
  			if (snumChars <= 0)
  				return -1;
  		}
  		return buf[curChar++];
  	}
  
  	public int nextInt() {
  		int c = read();
  		while (isSpaceChar(c)) {
  			c = read();
  		}
  		int sgn = 1;
  		if (c == '-') {
  			sgn = -1;
  			c = read();
  		}
  		int res = 0;
  		do {
  			res *= 10;
  			res += c - '0';
  			c = read();
  		} while (!isSpaceChar(c));
  		return res * sgn;
  	}
  
  	public long nextLong() {
  		int c = read();
  		while (isSpaceChar(c)) {
  			c = read();
  		}
  		int sgn = 1;
  		if (c == '-') {
  			sgn = -1;
  			c = read();
  		}
  		long res = 0;
  		do {
  			res *= 10;
  			res += c - '0';
  			c = read();
  		} while (!isSpaceChar(c));
  		return res * sgn;
  	}
  
  	public int[] nextIntArray(int n) {
  		int a[] = new int[n];
  		for (int i = 0; i < n; i++) {
  			a[i] = nextInt();
  		}
  		return a;
  	}
  
  	public String readString() {
  		int c = read();
  		while (isSpaceChar(c)) {
  			c = read();
  		}
  		StringBuilder res = new StringBuilder();
  		do {
  			res.appendCodePoint(c);
  			c = read();
  		} while (!isSpaceChar(c));
  		return res.toString();
  	}
  
  	public String nextLine() {
  		int c = read();
  		while (isSpaceChar(c))
  			c = read();
  		StringBuilder res = new StringBuilder();
  		do {
  			res.appendCodePoint(c);
  			c = read();
  		} while (!isEndOfLine(c));
  		return res.toString();
  	}
  
  	public boolean isSpaceChar(int c) {
  		return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
  	}
  
  	private boolean isEndOfLine(int c) {
  		return c == '\n' || c == '\r' || c == -1;
  	}
  
  }