source_code: import java.io.IOException;
  import java.io.InputStream;
  import java.io.PrintWriter;
  import java.util.InputMismatchException;
  
  public class C817{
  
  	void solve()
  	{
  		long n = nl(), s = nl();
  		long l = 0, r = n;
  		while(l < r)
  		{
  			long mid = (l + r)/2;
  			if(mid - digSum(mid) < s)
  				l = mid + 1;
  			else
  				r = mid;
  		}
  		out.println(l - digSum(l) >= s ? (n - l + 1) : 0);
  	}
  	
  	int digSum(long k)
  	{
  		int sum = 0;
  		while(k != 0)
  		{
  			sum += k % 10;
  			k /= 10;
  		}
  		return sum;
  	}
  	
  	public static void main(String[] args){new C817().run();}
  	
  	private byte[] bufferArray = new byte[1024];
  	private int bufLength = 0;
  	private int bufCurrent = 0;
  	InputStream inputStream;
  	PrintWriter out;
  	
  	public void run()
  	{
  		inputStream = System.in;
  		out = new PrintWriter(System.out);
  		solve();
  		out.flush();
  	}
  	
  	int nextByte()
  	{
  		if(bufLength==-1)
  			throw new InputMismatchException();
  		if(bufCurrent>=bufLength)
  		{
  			bufCurrent = 0;
  			try
  			{bufLength = inputStream.read(bufferArray);}
  			catch(IOException e)
  			{ throw new InputMismatchException();}
  			if(bufLength<=0)
  				return -1;
  		}
  		return bufferArray[bufCurrent++];
  	}
  	
  	boolean isSpaceChar(int x)
  	{return (x<33 || x>126);}
  	
  	boolean isDigit(int x)
  	{return (x>='0' && x<='9');}
  	
  	int nextNonSpace()
  	{
  		int x;
  		while((x=nextByte())!=-1 && isSpaceChar(x));
  		return x;
  	}
  	
  	int ni()
  	{
  		long ans = nl();
  		if ( Integer.MIN_VALUE <= ans && ans <= Integer.MAX_VALUE )
  			return (int)ans;
  		throw new InputMismatchException();
  	}
  	
  	long nl()
  	{
  		long ans = 0;
  		boolean neg = false;
  		int x = nextNonSpace();
  		if(x=='-') 
  		{
  			neg = true;
  			x = nextByte();
  		}
  		while(!isSpaceChar(x))
  		{
  			if(isDigit(x))
  			{
  				ans = ans*10 + x -'0';
  				x = nextByte();
  			}
  			else
  				throw new InputMismatchException();
  		}
  		return neg ? -ans:ans;
  	}
  	
  	String ns()
  	{
  		StringBuilder sb = new StringBuilder();
  		int x = nextNonSpace();
  		while(!isSpaceChar(x))
  		{
  			sb.append((char)x);
  			x = nextByte();
  		}
  		return sb.toString();
  	}
  	
  	char nc()
  	{ return (char)nextNonSpace();}
  	
  	double nd()
  	{ return (double)Double.parseDouble(ns()); }
  	
  	char[] ca()
  	{ return ns().toCharArray();}
  	
  	char[] ca(int n)
  	{
  		char[] ans = new char[n];
  		int p =0;
  		int x = nextNonSpace();
  		while(p<n)
  		{
  			ans[p++] = (char)x;
  			x = nextByte();
  		}
  		return ans;
  	}
  	
  	int[] ia(int n)
  	{
  		int[] ans = new int[n];
  		for(int i=0;i<n;i++)
  			ans[i]=ni();
  		return ans;
  	}
  	
  }
  