source_code: import java.io.BufferedReader;
  import java.io.FileNotFoundException;
  import java.io.FileReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.util.Arrays;
  import java.util.Random;
  import java.util.StringTokenizer;
  import java.util.TreeMap;
  
  public class P {
  
  	public static void main(String[] args) throws IOException {
  		Scanner sc = new Scanner(System.in);
  		long N = sc.nextLong(), S = sc.nextLong();
  		long lo = 0, hi = N;
  		long pivot = 0;
  		while (lo <= hi) {
  			long mid = lo + (hi - lo) / 2;
  			int sumOfDigits = 0;
  			long saveMid = mid;
  			while (saveMid > 0) {
  				sumOfDigits += saveMid % 10;
  				saveMid /= 10;
  			}
  			if (mid - sumOfDigits < S) {
  				pivot = mid;
  				lo = mid + 1;
  			} else
  				hi = mid - 1;
  		}
  
  		System.out.println(N - pivot);
  	}
  
  	static class Scanner {
  		StringTokenizer st;
  		BufferedReader br;
  
  		public Scanner(InputStream s) {
  			br = new BufferedReader(new InputStreamReader(s));
  		}
  
  		public Scanner(String f) throws FileNotFoundException {
  			br = new BufferedReader(new FileReader(f));
  		}
  
  		public String next() throws IOException {
  			while (st == null || !st.hasMoreTokens())
  				st = new StringTokenizer(br.readLine());
  			return st.nextToken();
  		}
  
  		public int nextInt() throws IOException {
  			return Integer.parseInt(next());
  		}
  
  		public long nextLong() throws IOException {
  			return Long.parseLong(next());
  		}
  
  		public String nextLine() throws IOException {
  			return br.readLine();
  		}
  
  		public double nextDouble() throws IOException {
  			return Double.parseDouble(next());
  		}
  
  		public boolean ready() throws IOException {
  			return br.ready();
  		}
  
  		public int[] nextIntArray(int n) throws IOException {
  			int[] a = new int[n];
  			for (int i = 0; i < n; i++)
  				a[i] = nextInt();
  			return a;
  		}
  
  		public int[] nextIntArray1(int n) throws IOException {
  			int[] a = new int[n + 1];
  			for (int i = 1; i <= n; i++)
  				a[i] = nextInt();
  			return a;
  		}
  
  		public int[] shuffle(int[] a, int n) {
  			int[] b = new int[n];
  			for (int i = 0; i < n; i++)
  				b[i] = a[i];
  			Random r = new Random();
  			for (int i = 0; i < n; i++) {
  				int j = i + r.nextInt(n - i);
  				int t = b[i];
  				b[i] = b[j];
  				b[j] = t;
  			}
  			return b;
  		}
  
  		public int[] nextIntArraySorted(int n) throws IOException {
  			int[] a = nextIntArray(n);
  			a = shuffle(a, n);
  			Arrays.sort(a);
  			return a;
  		}
  
  		public long[] nextLongArray(int n) throws IOException {
  			long[] a = new long[n];
  			for (int i = 0; i < n; i++)
  				a[i] = nextLong();
  			return a;
  		}
  
  		public long[] nextLongArray1(int n) throws IOException {
  			long[] a = new long[n + 1];
  			for (int i = 1; i <= n; i++)
  				a[i] = nextLong();
  			return a;
  		}
  
  		public long[] nextLongArraySorted(int n) throws IOException {
  			long[] a = nextLongArray(n);
  			Random r = new Random();
  			for (int i = 0; i < n; i++) {
  				int j = i + r.nextInt(n - i);
  				long t = a[i];
  				a[i] = a[j];
  				a[j] = t;
  			}
  			Arrays.sort(a);
  			return a;
  		}
  	}
  
  }