source_code: import java.math.BigDecimal;
  import java.util.Scanner;
  
  public class ReallyBigNumbers {
  
  	public static void main(String[] args) {
  		Scanner scan = new Scanner(System.in);
  		long n = scan.nextLong();
  		long s = scan.nextLong();
  		long ans = 0;
  		long l = 0;
          long r = n;
          while (l <= r) {
              // Key is in a[lo..hi] or not present.
              long mid = l + (r - l) / 2;
              if(isReallyBig(mid, s)){
              	ans = mid;
              	r = mid-1;
              }
              else l = mid+1;
          }
          if(ans == 0) System.out.println(ans);
          else
          	System.out.println(n-ans+1);
  	}
  	
  	static boolean isReallyBig(long m, long s){
  		String x = m+"";
  		long sum = 0;
  		for(int i = 0; i < x.length(); i++){
  			sum += x.charAt(i)-'0';
  		}
  		if(m-sum >= s) return true;
  		return false;
  	}
  }
  