source_code: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.util.StringTokenizer;
  
  public class C {
  
  	public static void main(String[] args) throws InterruptedException{
  		FastScanner scan = new FastScanner();
  		PrintWriter out = new PrintWriter(System.out);
  		long n = scan.nextLong(), s = scan.nextLong();
  		long lo = 1, hi = n+1;
  		for(int bs = 0; bs < 100; bs++) {
  			long mid = (lo+hi)>>1;
  			long mid2 = mid;
  			long c = 0;
  			while(mid > 0) {
  				c += mid%10;
  				mid /= 10;
  			}
  			if(mid2-c < s) lo = mid2;
  			else hi = mid2;
  		}
  		out.println(n-lo);
  		out.close();
  	}
  
  	static class FastScanner {
  		BufferedReader br;
  		StringTokenizer st;
  
  		public FastScanner() {
  			try	{
  				br = new BufferedReader(new InputStreamReader(System.in));
  				st = new StringTokenizer(br.readLine());
  			} catch (Exception e){e.printStackTrace();}
  		}
  
  		public String next() {
  			if (st.hasMoreTokens())	return st.nextToken();
  			try {st = new StringTokenizer(br.readLine());}
  			catch (Exception e) {e.printStackTrace();}
  			return st.nextToken();
  		}
  
  		public int nextInt() {return Integer.parseInt(next());}
  
  		public long nextLong() {return Long.parseLong(next());}
  
  		public double nextDouble() {return Double.parseDouble(next());}
  
  		public String nextLine() {
  			String line = "";
  			if(st.hasMoreTokens()) line = st.nextToken();
  			else try {return br.readLine();}catch(IOException e){e.printStackTrace();}
  			while(st.hasMoreTokens()) line += " "+st.nextToken();
  			return line;
  		}
  
  		public int[] nextIntArray(int n) {
  			int[] a = new int[n];
  			for(int i = 0; i < n; i++) a[i] = nextInt();
  			return a;
  		}
  
  		public long[] nextLongArray(int n){
  			long[] a = new long[n];
  			for(int i = 0; i < n; i++) a[i] = nextLong();
  			return a;
  		}
  
  		public double[] nextDoubleArray(int n){
  			double[] a = new double[n];
  			for(int i = 0; i < n; i++) a[i] = nextDouble();
  			return a;
  		}
  
  		public char[][] nextGrid(int n, int m){
  			char[][] grid = new char[n][m];
  			for(int i = 0; i < n; i++) grid[i] = next().toCharArray();
  			return grid;
  		}
  	}
  
  }
  