The number on the board

给出两个正整数 $k,n$，其中的 $n$ 被修改过，你需要修改 $n$ 中的某几位，使新的 $n$ 的各个位置的和不小于 $k$，求最小的修改次数。

Some natural number was written on the board. Its sum of digits was not less than $ k $ . But you were distracted a bit, and someone changed this number to $ n $ , replacing some digits with others. It's known that the length of the number didn't change. You have to find the minimum number of digits in which these two numbers can differ.

The first line contains integer $ k $ ( $ 1<=k<=10^{9} $ ). The second line contains integer $ n $ ( $ 1<=n&lt;10^{100000} $ ). There are no leading zeros in $ n $ . It's guaranteed that this situation is possible.

Print the minimum number of digits in which the initial number and $ n $ can differ.

3
11

1

3
99

0

In the first example, the initial number could be $ 12 $ . In the second example the sum of the digits of $ n $ is not less than $ k $ . The initial number could be equal to $ n $ .