source_code: import java.util.Scanner;
  
  public class Test {
  	
  	private static long sum(long value) {
  		long ans = 0;
  		while (value > 0) {
  			ans += value % 10;
  			value /= 10;
  		}
  		return ans;
  	}
  	
  	public static void main(String[] args) {
  		
  		Scanner scan = new Scanner(System.in);
  		long n , s , ans = 0;
  		n = scan.nextLong();
  		s = scan.nextLong();
  		long current = s;
  		while (current <= n && current <= s + 20 * 9) {
  			// current - sum(current) >= s
  			long temp = sum(current);
  			if (current - temp >= s) {
  				ans ++;
  			}
  			current ++;
  		}
  		if (current <= n) {
  			ans += (n - current + 1);
  		}
  		System.out.println(ans);
  		
  	}
  	
  		
  }
  	
  	
  	
  	
  	
  
  
  
  
  
  
  
  