CF835B.The number on the board

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.

黑板上写了一个自然数，其各位数字之和不小于 $k$。但你稍一分神，有人将这个数改成了 $n$，即用其他数字替换了其中若干位数字。已知该数的位数未发生变化。

你需要求出这两个数在最少多少位数字上不同。

The first line contains integer k (1 ≤ k ≤ 109).

The second line contains integer n (1 ≤ n < 10100000).

There are no leading zeros in n. It's guaranteed that this situation is possible.

第一行包含一个整数 $k$（$1 \leq k \leq 10^9$）。

第二行包含一个整数 $n$（$1 \leq n < 10^{100000}$）。

$n$ 不含前导零。题目保证该情况是可能的。

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

输出初始数字与 n 在多少位数字上存在差异的最小值。

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.

在第一个例子中，初始数字可以是 12。

在第二个例子中，$ n $ 的各位数字之和不小于 $ k $。初始数字可以等于 $ n $。