source_code: import java.io.*;
  import java.math.BigInteger;
  import java.util.*;
  	
  public 	class a {
  		public static void main(String args[])throws IOException{
  		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  		OutputStream out=new BufferedOutputStream(System.out);
  		String s[]=br.readLine().trim().split("\\ ");
  		BigInteger a1=new BigInteger(s[0]);
  		BigInteger a=new BigInteger(s[0]);
  		String q=a.toString();
  		String q1=q.substring(q.length()-1, q.length());
  		a=a.subtract(new BigInteger(q1));
  		//System.out.println(a.toString());
  		BigInteger c=new BigInteger("1");
  		BigInteger b=new BigInteger(s[1]);
  		int z=check(a,a.toString(),b);
  		if(z==1)
  		{
  			out.write("0".getBytes());
  			out.flush();
  			//System.out.println("jwefcyuwe");
  			return;
  		}
  		while(a.compareTo(c)>0)
  		{
  			BigInteger d=a;
  			if(d.subtract(c).compareTo(new BigInteger("9"))==-1)
  			{
  				break;
  			}
  			else
  			{
  				BigInteger mid=a;
  				mid=mid.add(c);
  				mid=mid.divide(new BigInteger("2"));
  				//System.out.println(mid.toString());
  				if(check(mid,mid.toString(),b)==1)
  				{
  					c=mid;
  					c=c.add(new BigInteger("1"));
  				}
  				else
  				{
  					a=mid;
  					
  					//System.out.println(a.toString());
  				}
  					
  			}
  			
  		}
  		 q=a.toString();
  		 q1=q.substring(q.length()-1, q.length());
  		a=a.subtract(new BigInteger(q1));
  		BigInteger ans=a1.subtract(a);
  		ans=ans.add(new BigInteger("1"));
  		out.write(ans.toString().getBytes());
  		//System.out.print("sfvlksfv");
  		
  		
  		out.flush();
  	}
  		
  		static int check(BigInteger a,String s,BigInteger b)
  		{
  			int l=s.length();
  			long z=0;
  			for(int i=0;i<l;i++)
  			{
  				z+=Long.parseLong(s.substring(i,i+1));
  			}
  			BigInteger c=a.subtract(new BigInteger(Long.toString(z)));
  			//System.out.println(c.toString());
  			return -1*c.compareTo(b);
  		}
  	}