source_code: import java.io.*;
  import java.util.*;
  
  /**
   *
   * @author Jishnu_T
   */
  public class ReallyBigNums {
      
      private static long[] factorArray(long s)
      {
          int d=0;
          long n=s;
          long f=1;
          while(n>0)
          {
              n=n/10;
              d++;
              f = f*10;
          }
          
          long[] fact = new long[d+1];
          n=s;
          for(int i=d;i>=0;i--)
          {
              if(f==1)
                  fact[i] = n;
              else
              {
                  fact[i] = n/(f-1);
                  n = n%(f-1);
                  f=f/10;
              }
          }
          int carry=0;
          for(int i=0;i<=d;i++)
          {
              fact[i] = fact[i]+carry;
              if(fact[i]>9 || (i==0 && fact[i]>0))
              {
                  fact[i] = 0;
                  carry = 1;
                  for(int j=i-1;j>=0;j--)
                  {
                      fact[j] =0;
                  }
              }
              else
              {
                  carry = 0;
              }
          }
          
          return fact;
      }
      
      private static long bigNumCount(long n, long s)
      {
          if(s>=n)
              return 0;
          if(s==0)
              return n;
          long[] fact = factorArray(s);
          
          long startNum = 0;
          int len = fact.length;
          long tenPow = 1;
          for(int i=0;i<len;i++)
          {
              startNum = startNum+tenPow*fact[i];
              tenPow = tenPow*10;
          }
          
          return(Math.max(0,n-startNum+1));
      }
      private static class FastReader
      {
          BufferedReader br;
          StringTokenizer st;
   
          public FastReader()
          {
              br = new BufferedReader(new
                       InputStreamReader(System.in));
          }
   
          String next()
          {
              while (st == null || !st.hasMoreElements())
              {
                  try
                  {
                      st = new StringTokenizer(br.readLine());
                  }
                  catch (IOException  e)
                  {
                      e.printStackTrace();
                  }
              }
              return st.nextToken();
          }
   
          int nextInt()
          {
              return Integer.parseInt(next());
          }
   
          long nextLong()
          {
              return Long.parseLong(next());
          }
   
          double nextDouble()
          {
              return Double.parseDouble(next());
          }
   
          String nextLine()
          {
              String str = "";
              try
              {
                  str = br.readLine();
              }
              catch (IOException e)
              {
                  e.printStackTrace();
              }
              return str;
          }
      }
      public static void main(String args[])
      {
          FastReader r = new FastReader();
          long n = r.nextLong();
          long s=  r.nextLong();
          System.out.println(bigNumCount(n,s));
      }
      
  }
  