source_code: /**
   * DA-IICT
   * Author : Savaliya Sagar
   */
  import java.io.*;
  import java.math.*;
  import java.util.*;
  
  public class C817 {
  	InputStream is;
  	PrintWriter out;
  	String INPUT = "";
  
  	void solve() {
  		long n = nl();
  		long s = nl();
  		long l = 1;
  		long r = n;
  		long ans = 0;
  		while(l<=r){
  			long mid = (l+r)/2;
  			long sum = 0;
  			long temp = mid;
  			while(temp!=0){
  				sum += temp%10;
  				temp/=10;
  			}
  			if(mid-sum<s){
  				ans = mid;
  				l = mid+1;
  			}else
  				r = mid - 1;
  		}
  		out.println(n-ans);
  	}
  
  	void run() throws Exception {
  		is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
  		out = new PrintWriter(System.out);
  
  		long s = System.currentTimeMillis();
  		solve();
  		out.flush();
  		if (!INPUT.isEmpty())
  			tr(System.currentTimeMillis() - s + "ms");
  	}
  
  	public static void main(String[] args) throws Exception {
  		new Thread(null, new Runnable() {
  			public void run() {
  				try {
  					new C817().run();
  				} catch (Exception e) {
  					e.printStackTrace();
  				}
  			}
  		}, "1", 1 << 26).start();
  	}
  
  	private byte[] inbuf = new byte[1024];
  	public int lenbuf = 0, ptrbuf = 0;
  
  	private int readByte() {
  		if (lenbuf == -1)
  			throw new InputMismatchException();
  		if (ptrbuf >= lenbuf) {
  			ptrbuf = 0;
  			try {
  				lenbuf = is.read(inbuf);
  			} catch (IOException e) {
  				throw new InputMismatchException();
  			}
  			if (lenbuf <= 0)
  				return -1;
  		}
  		return inbuf[ptrbuf++];
  	}
  
  	private boolean isSpaceChar(int c) {
  		return !(c >= 33 && c <= 126);
  	}
  
  	private int skip() {
  		int b;
  		while ((b = readByte()) != -1 && isSpaceChar(b))
  			;
  		return b;
  	}
  
  	private double nd() {
  		return Double.parseDouble(ns());
  	}
  
  	private char nc() {
  		return (char) skip();
  	}
  
  	private String ns() {
  		int b = skip();
  		StringBuilder sb = new StringBuilder();
  		while (!(isSpaceChar(b))) { // when nextLine, (isSpaceChar(b) && b !=
  										// ' ')
  			sb.appendCodePoint(b);
  			b = readByte();
  		}
  		return sb.toString();
  	}
  
  	private char[] ns(int n) {
  		char[] buf = new char[n];
  		int b = skip(), p = 0;
  		while (p < n && !(isSpaceChar(b))) {
  			buf[p++] = (char) b;
  			b = readByte();
  		}
  		return n == p ? buf : Arrays.copyOf(buf, p);
  	}
  
  	private char[][] nm(int n, int m) {
  		char[][] map = new char[n][];
  		for (int i = 0; i < n; i++)
  			map[i] = ns(m);
  		return map;
  	}
  
  	private int[] na(int n) {
  		int[] a = new int[n];
  		for (int i = 0; i < n; i++)
  			a[i] = ni();
  		return a;
  	}
  
  	private int ni() {
  		int num = 0, b;
  		boolean minus = false;
  		while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'))
  			;
  		if (b == '-') {
  			minus = true;
  			b = readByte();
  		}
  
  		while (true) {
  			if (b >= '0' && b <= '9') {
  				num = num * 10 + (b - '0');
  			} else {
  				return minus ? -num : num;
  			}
  			b = readByte();
  		}
  	}
  
  	private long nl() {
  		long num = 0;
  		int b;
  		boolean minus = false;
  		while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'))
  			;
  		if (b == '-') {
  			minus = true;
  			b = readByte();
  		}
  
  		while (true) {
  			if (b >= '0' && b <= '9') {
  				num = num * 10 + (b - '0');
  			} else {
  				return minus ? -num : num;
  			}
  			b = readByte();
  		}
  	}
  
  	private void tr(Object... o) {
  		System.out.println(Arrays.deepToString(o));
  	}
  }
  