Problem:
Score : 300 points

Problem Statement

There are N stones arranged in a row. Every stone is painted white or black.
A string S represents the color of the stones. The i-th stone from the left is white if the i-th character of S is ., and the stone is black if the character is #.

Takahashi wants to change the colors of some stones to black or white so that there will be no white stone immediately to the right of a black stone.
Find the minimum number of stones that needs to be recolored.

Constraints

1 \leq N \leq 2\times 10^5

S is a string of length N consisting of . and #.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the minimum number of stones that needs to be recolored.

Sample Input 1

3
#.#

Sample Output 1

1

It is enough to change the color of the first stone to white.

Sample Input 2

5
#.##.

Sample Output 2

2

Sample Input 3

9
.........

Sample Output 3

0

Solution in OCaml (4.02.3) (judge verdict: Wrong Answer)

let split_string ?(pattern="") = Str.split @@ Str.regexp pattern
let n = Scanf.sscanf (read_line ()) "%d" @@ fun n -> n
let s = read_line () |> split_string
let () = Printf.printf "%d\n" @@ snd @@ List.fold_left (fun (b, sum) ch -> (b || ch = "#", sum + if b && ch = "#" then 1 else 0)) (false, 0) s