AT_abc468_b.Corridor Watch

You are given integers $M,D$ and a string $S$ of length $M$ consisting of G and ..

There are $M$ cells arranged in a row from left to right, numbered $1$ through $M$ from the left.

Some of the cells have a guardman standing on them. Specifically, a guardman stands on cell $i$ if $S_i=$ G, and no one stands on cell $i$ if $S_i=$ ..

A cell whose distance from a cell with a guardman is at most $D$ is watched by that guardman. That is, a cell $x$ is watched by a guardman if there exists a cell $i$ such that $S_i=$ G and $|x-i|\le D$.

Among the $M$ cells, find the number of cells that are not watched.

给你整数 $M$、$D$ 和一个长度为 $M$ 的字符串 $S$，其中只包含字符 G 和 .。

从左到右依次排列着 $M$ 个格子，编号从左至右为 $1$ 到 $M$。

部分格子上站着守卫。具体而言：若 $S_i=$ G，则第 $i$ 个格子上站着一名守卫；若 $S_i=$ .，则第 $i$ 个格子上无人。

若某个格子与某守卫所在格子的距离不超过 $D$，则该格子被该守卫监视。即：格子 $x$ 被某守卫监视，当且仅当存在某个格子 $i$ 满足 $S_i=$ G 且 $|x-i|\le D$。

在全部 $M$ 个格子中，求未被监视的格子数量。

The input is given from Standard Input in the following format:

$M$ $D$
$S$

输入从标准输入以如下格式给出：

$M$ $D$
$S$

Output the answer.

输出答案。

Sample 1 Explanation:
Only cell $4$ is not watched.

Sample 2 Explanation:
All cells are not watched.

Constraints

• $0\le D < M \le 100$
• $D$ and $M$ are integers.
• $S_i$ is a string of length $M$ consisting of G and ..

样例 1 解释：
只有第 $4$ 个格子未被监视。

样例 2 解释：
所有格子均未被监视。

约束条件

• $0\le D < M \le 100$
• $D$ 和 $M$ 均为整数。
• $S_i$ 是一个长度为 $M$ 的字符串，仅由字符 G 和 . 组成。