source_code: import java.util.Scanner;
  import java.io.*;
  import java.util.*;
  import java.math.*;
  import java.lang.*;
  import static java.lang.Math.*;
  
  public class main implements Runnable{
  
      static ArrayList <Integer> adj[];
      static int co=0,f=0;
  
      static void Check2(int n){
          adj=new ArrayList[n+1];
          for(int i=0;i<=n;i++){
              adj[i]=new ArrayList<>();
          }
  
      }
      static void add(int i,int j){
  
          adj[i].add(j);
          adj[j].add(i);
      }
      public static void main(String[] args)  {
          new Thread(null, new main(), "Check2", 1<<26).start();// to increse stack size in java
      }
      static long mod=(long)(1e9+7);
      public void run() {
          /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
          //Scanner in=new Scanner(System.in);
  
          InputReader in = new InputReader(System.in);
          PrintWriter w = new PrintWriter(System.out);
  
  
  
         long n=in.nextLong();
          long s=in.nextLong();
          
          long l=1;
          long r=(long)(n);
         long ans=-1;
          while(l<=r){
              
              long mid=(l+r)/2;
              if(ch(mid,s)){
                  ans=mid;
                  r=mid-1;
              }
              else
              {
                  l=mid+1;
              }
              
          }
          if(ans==-1)w.println(0);
          else
              w.println(n-ans+1);
          w.close();
      }
          public boolean ch(long a,long s){
              
              long p=0;
              long val=a;
              while(val>0){
                  p=p+val%10;
                  val=val/10;
              }
              if(a-p>=s)return true;
              return false;
              
          }
      public boolean rec(int a,int b,int x,int y,int c,int d,int co){
  
          if(a>x|b>y)return false;
  
          if(a<-100000||b<-100000||co>100000)return false;
  
          if(a==x&&b==y)return true;
  
  
  
          return (rec(a+c,b+d,x,y,c,d,co+1)||rec(a+c,b-d,x,y,c,d,co+1)||rec(a-c,b+d,x,y,c,d,co+1)||rec(a-c,b-d,x,y,c,d,co+1));
  
  
  
      }
  
  
  
      static  int gcd(int a,int b){
  
          if(b==0)return a;
          return gcd(b,a%b);
      }
      static  void dfs(int i,int v[],int val,int b[]){
  
  
          if(v[i]==1)return ;
  
          v[i]=1;
          b[i]=val;
  
          Iterator <Integer> it=adj[i].iterator();
          while(it.hasNext()){
              int q=it.next();
              dfs(q,v,val,b);
          }
  
  
  
  
  
      }
  
      static  void sev(int a[],int n){
  
          for(int i=2;i<=n;i++)a[i]=i;
          for(int i=2;i<=n;i++){
  
              if(a[i]!=0){
                  for(int j=2*i;j<=n;){
  
                      a[j]=0;
                      j=j+i;
                  }
              }
  
          }
  
      }
  
      static class pair implements Comparable<pair> {
  
          int x,y;
          pair(int c,int d){
              x=c;
              y=d;
          }
  
          public int compareTo(pair o){
  
              return (this.x-o.x);   //sort in incrementing order w.r.t to c
          }
  
  
  
      }
  
      static class node{
  
          int y;
          int val;
  
          node(int a,int b){
  
              y=a;
              val=b;
  
          }
  
  
      }
      static  void rec(String s,int a,int b,int n){
  
          if(b==n){
              System.out.println(s);
              return ;
          }
          String p=s;
          if(a>b){
              s=p+")" ;
              rec(s,a,b+1,n);
          }
          if(a<n){
              s=p+"(";
              rec(s,a+1,b,n);
          }
  
  
  
  
      }
  
      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);
          }
      }
  
  
  
  
  
  
  
  }