package main

import (
	"fmt"
)

func main() {
	var n, s int64
	if _, err := fmt.Scan(&n, &s); err != nil {
		return
	}

	left := int64(1)
	right := n + 1
	ans := n + 1

	for left <= right {
		mid := left + (right-left)/2
		sum := int64(0)
		temp := mid
		for temp > 0 {
			sum += temp % 10
			temp /= 10
		}
		if mid-sum >= s {
			ans = mid
			right = mid - 1
		} else {
			left = mid + 1
		}
	}

	res := n - ans + 1
	if res < 0 {
		res = 0
	}
	fmt.Println(res)
}