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 Haskell (GHC 7.10.3) (judge verdict: Wrong Answer)

import Data.List.Split

main = do 
    n <- readLn :: IO Int
    s <- getLine
    let ts = reverse $ dropWhile (\x-> x == '#') $ reverse $ dropWhile (\x-> x == '.') s
    let spS = splitOn "#" ts
    let res = map (\x-> cnt x (1,0)) spS
    --print $ res
    print $ sum $ map (\x->min (fst x) (snd x)) res

cnt :: String -> (Int,Int) -> (Int, Int)
cnt [] (b,w) = (b,w)
cnt (x:xs) (b,w) = if x == '#' then cnt xs (b+1,w) else cnt xs(b,w+1)