source_code: import java.util.Scanner;
  
  public class ReallyBigNumbers {
  	public static void main(String[] args) {
  		@SuppressWarnings("resource")
  		Scanner sc = new Scanner(System.in);
  		long n = sc.nextLong(); // max
  		long s = sc.nextLong(); // differential
  		long bigNums = 0;
  		long inARow = 0;
  		for (long i = s; i <= n; i++) {
  			if (inARow == 9) {
  				bigNums += (n - i+1);
  				break;
  			} else {
  				if (i >= s + digitSum(i)) {
  					bigNums++;
  					inARow++;
  				} else {
  					inARow = 0;
  				}
  			}
  		}
  		System.out.println(bigNums);
  	}
  
  	public static long digitSum(long a) {
  		long sum = a % 10;
  		if (9 < a) {
  			a /= 10;
  			sum += digitSum(a);
  		}
  		return sum;
  	}
  }
  