source_code: import java.io.IOException;
  import java.io.InputStream;
  import java.io.PrintWriter;
  import java.util.InputMismatchException;
  import java.util.*;
  
  public class ed817Q3 {
  	public static void main(String[] args){
  		InputReader in = new InputReader(System.in);
  		PrintWriter out = new PrintWriter(System.out);
  		int t = 1;
  		for(int zxz=0;zxz<t;zxz++){
  			// my code starts here
  			long n = in.nextLong();
  			long s = in.nextLong();
  			long start=0,end=n;
  			long ans=n+1;
  			while(start<=end){
  				long mid = start+(end-start)/2;
  				if(mid-digitSum(mid)>=s){
  					ans = mid;
  					end = mid-1;
  				}
  				else{
  					start=mid+1;
  				}
  			}
  			System.out.println(n-ans+1);
  			// my code ends here
  		}
  	}
  	static int digitSum(long n){
  		int sum=0;
  		while(n>0){
  			sum+=n%10;
  			n=n/10;
  		}
  		return sum;
  	}
  	static class InputReader {
  		 
          private InputStream stream;
          private byte[] buf = new byte[8192];
          private int curChar, snumChars;
          private SpaceCharFilter filter;
   
          public InputReader(InputStream stream) {
              this.stream = stream;
          }
   
          public int snext() {
              if (snumChars == -1)
                  throw new InputMismatchException();
              if (curChar >= snumChars) {
                  curChar = 0;
                  try {
                      snumChars = stream.read(buf);
                  } catch (IOException e) {
                      throw new InputMismatchException();
                  }
                  if (snumChars <= 0)
                      return -1;
              }
              return buf[curChar++];
          }
   
          public int nextInt() {
              int c = snext();
              while (isSpaceChar(c))
                  c = snext();
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = snext();
              }
              int res = 0;
              do {
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = snext();
              } while (!isSpaceChar(c));
              return res * sgn;
          }
   
          public long nextLong() {
              int c = snext();
              while (isSpaceChar(c))
                  c = snext();
              int sgn = 1;
              if (c == '-') {
                  sgn = -1;
                  c = snext();
              }
              long res = 0;
              do {
                  if (c < '0' || c > '9')
                      throw new InputMismatchException();
                  res *= 10;
                  res += c - '0';
                  c = snext();
              } while (!isSpaceChar(c));
              return res * sgn;
          }
   
          public int[] nextIntArray(int n) {
              int a[] = new int[n];
              for (int i = 0; i < n; i++)
                  a[i] = nextInt();
              return a;
          }
   
          public String readString() {
              int c = snext();
              while (isSpaceChar(c))
                  c = snext();
              StringBuilder res = new StringBuilder();
              do {
                  res.appendCodePoint(c);
                  c = snext();
              } 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 interface SpaceCharFilter {
              public boolean isSpaceChar(int ch);
          }
      }
  }
  