source_code: import java.util.*;
  import java.io.*;
  import java.lang.Math.*;
  
  public class Main{
  	static long s;
  	static boolean check(long n){
  		int sum = 0;
  		long storen=n;
  		while(n>0){
  			int k = (int)(n%10);
  			n /=10;
  			sum+=k;
  		}
  		return storen-(long)sum >= s;
  	}
  	public static void main(String args[]){
  		PrintWriter pw=new PrintWriter(System.out);
  		InputReader ip=new InputReader(System.in);
  		
  		long n;
  		n=ip.nextLong();
  		s=ip.nextLong();
  
  		if(s>n){
  			pw.println("0");
  		}
  		else{
  			long l=0,r=n;
  			boolean possible=false;
  			long mid=0;
  			int it=100;
  			while(it-->0){
  				mid = (l+r)/2;
  				if(check(mid)){
  					r=mid;
  					possible = true;
  				}
  				else{
  					l=mid+1;
  				}
  		//		pw.println(mid);
  		//		pw.println(l+" "+r);
  			}
  			if(possible){
  				pw.println(n-l+1);
  			}	
  			else{
  				pw.println("0");
  			}
  		}
  		
  		pw.close();
  	}
  	static class InputReader {
          private InputStream stream;
          private byte[] buf = new byte[1024];
          private int curChar;
          private int numChars;
          private SpaceCharFilter filter;
  
          public InputReader(InputStream stream) {
              this.stream = stream;
          }
  
          public int read() {
              if (numChars == -1)
                  throw new InputMismatchException();
  
              if (curChar >= numChars) {
                  curChar = 0;
                  try {
                      numChars = stream.read(buf);
                  } catch (IOException e) {
                      throw new InputMismatchException();
                  }
  
                  if (numChars <= 0)
                      return -1;
              }
              return buf[curChar++];
          }
  
          public String nextLine() {
              BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
              String str = "";
              try {
                  str = br.readLine();
              } catch (IOException e) {
                  e.printStackTrace();
              }
              return str;
          }
  
          public int nextInt() {
              int c = read();
  
              while (isSpaceChar(c))
                  c = read();
  
              int sgn = 1;
  
              if (c == '-') {
                  sgn = -1;
                  c = read();
              }
  
              int res = 0;
              do {
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  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 {
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = read();
              }
              while (!isSpaceChar(c));
              return res * sgn;
          }
  
          public double nextDouble() {
              int c = read();
              while (isSpaceChar(c))
                  c = read();
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = read();
              }
              double res = 0;
              while (!isSpaceChar(c) && c != '.') {
                  if (c == 'e' || c == 'E')
                      return res * Math.pow(10, nextInt());
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = read();
              }
              if (c == '.') {
                  c = read();
                  double m = 1;
                  while (!isSpaceChar(c)) {
                      if (c == 'e' || c == 'E')
                          return res * Math.pow(10, nextInt());
                      if (c < '0' || c > '9')
                          throw new InputMismatchException();
                      m /= 10;
                      res += (c - '0') * m;
                      c = read();
                  }
              }
              return res * sgn;
          }
  
          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 boolean isSpaceChar(int c) {
              if (filter != null)
                  return filter.isSpaceChar(c);
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
  
          public String next() {
              return readString();
          }
  
          public interface SpaceCharFilter {
              public boolean isSpaceChar(int ch);
          }
      }
  }