source_code: import java.util.Scanner;
  
  public class C {
  	public static void main(String[] args) {
  
  		Scanner scan = new Scanner(System.in);
  
  		long n = scan.nextLong();
  		long s = scan.nextLong();
  		long low = 0;
  		long high = n + 1;
  		while (high-low>1) {
  			long sum = 0;
  			long mid = (high + low) / 2;
  			long value = findSum(mid, sum);
  			if (mid - value >= s)
  				high = mid;
  			else
  				low = mid;
  		}
  		
  		System.out.println(n - high + 1);
  
  		scan.close();
  	}
  
  	public static long findSum(long n, long sum) {
  		if (n == 0)
  			return sum;
  		return findSum(n / 10, sum + n % 10);
  	}
  
  }