source_code: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  
  public class Main {
  
  	public static void main(String[] args) throws IOException {
  
  		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  		String[] in = br.readLine().split(" ");
  		long n = Long.parseLong(in[0]), s = Long.parseLong(in[1]);
  		Solver solver = new Solver(n, s);
  		System.out.println(solver.solve());
  
  	}
  
  }
  
  class Solver {
  
  	private long n, s;
  
  	Solver(long n, long s) {
  		this.n = n;
  		this.s = s;
  	}
  
  	public long solve() {
  		long low = 1, high = n;
  		for (int i = 0; i < 72; ++i) {
  			long x = low + (high - low) / 2;
  			if (check(x))
  				high = x - 1;
  			else
  				low = x + 1;
  		}
  		return n - high;
  	}
  
  	private boolean check(long x) {
  
  		long tmp = x;
  		int sum = 0;
  		while (tmp > 0) {
  			sum += tmp % 10;
  			tmp /= 10;
  		}
  		return x - sum >= s;
  	}
  }
  