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.math.BigInteger;
  import java.util.Arrays;
  import java.util.Random;
  import java.util.StringTokenizer;
  
  public class Edu23 {
  
  	public static int sum(String s){
  		int tot=0;
  		for(int i =0; i<s.length();i++){
  			tot+=(s.charAt(i)-'0');
  		}
  		return tot;
  	}
  	public static BigInteger comb(int n, int k){
  		if(k==0)
  			return new BigInteger("1");
  		else
  			return comb(n,k-1).multiply(new BigInteger(n-k+1+"")).divide(new BigInteger(k+""));
  	}
  	public static void main(String[] args) throws IOException {
  		Scanner sc = new Scanner(System.in);
  		long n = sc.nextLong();
  		long s = sc.nextLong();
  		long i;
  		for(i =s ; i-sum(i+"")<s;i++)
  			if(i%10==0)i+=9;
  		System.out.println(Math.max(0, n-i+1));
  		
  	}
  	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;
  		}
  	}
  }
  