source_code: import java.io.IOException;
  import java.io.InputStream;
  import java.util.InputMismatchException;
  
  public class ques3 {
  	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 static boolean isWhitespace(int c) {
              return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
          }
   
          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 boolean isSpaceChar(int c) {
              if (filter != null) {
                  return filter.isSpaceChar(c);
              }
              return isWhitespace(c);
          }
   
          public interface SpaceCharFilter {
   
              public boolean isSpaceChar(int ch);
          }
   
          public String next() {
              return nextString();
          }
          
          public char nextChar(){
          	int c=read();
          	while (isSpaceChar(c)) {
                  c = read();
              }
          	return (char)c;
          }
   
          public String nextString() {
              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 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() {
              return Long.parseLong(nextString());
          }
   
          public Double nextDouble() {
              return Double.parseDouble(nextString());
          }
      }
  
  	public static void main(String[] args) {
  		InputReader sc=new InputReader(System.in);
  		long n=sc.nextLong();
  		long s=sc.nextLong();
  		
  		long start=0,end=n;
  		while(start<end)
  		{
  			long mid=(start+end)/2;
  			if(func(mid)>=s)
  				end=mid;
  			else 
  				start=mid+1;
  		}
  		if(func(start)>=s)
  			System.out.println(n-start+1);
  		else
  			System.out.println(0);
  	}
  	
  	public static long func(long n)
  	{
  		long temp=n;
  		int sum=0;
  		while(temp>0)
  		{
  			sum+=temp%10;
  			temp/=10;
  		}
  		return n-sum;
  	}
  }