source_code: import java.util.Scanner;
  
  public class C {
  	
  	public static void main(String[] args) {
  		new C();
  	}
  
  	C() {
  		
  		Scanner in = new Scanner(System.in);
  		
  		long n = in.nextLong(), s = in.nextLong();
  		long lo = 1, hi = 1000000000000000000L;
  		
  		while(lo<hi){
  			//System.out.println(lo+" "+hi);
  			//STUPID STUPID DUMB
  			long mid = (lo+hi)/2;
  			if(reallyBig(mid,s))
  				hi = mid;
  			else
  				lo = mid+1;
  		}
  		
  		//System.out.println(lo+" "+hi);
  		if(!reallyBig(lo,s))
  			System.out.println(0);
  		else
  			System.out.println(Math.max(n-lo+1,0));
  			
  		//System.out.println(reallyBig(100000000000000009L,100000000000000000L));
  
  		in.close();
  
  	}
  	
  	boolean reallyBig(long n, long s){
  		int sum = 0;
  		long temp = n;
  		while(temp>0){
  			sum += temp%10;
  			temp/=10;
  		}
  		return n-sum>=s;
  	}
  	
  }
  
  /*
  
  12 1
  
  25 20
  
  10 9
  
  1000000000000000000 1000000000000000000
  
  1000000000000000000 100000000000000000
  
   */
  
  
  
  
  
  
  
  
  
  