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 Python (3.8.2) (judge verdict: Wrong Answer)

n=int(input())
from itertools import groupby

s=list(input())

gr=groupby(s)

#flg=0:白の状態
cnt=0
flg=0
bflg=0
for k,v in gr:
    if flg==0:
        if k=='#':
            flg=1
            b=len(list(v))
    else:
        if k=='.':
            w=len(list(v))
            if bflg==0:
                if b>=w:
                    cnt+=w
                    bflg=1
                else:
                    cnt+=b
            else:
                cnt+=w
                bflg=0

            flg=0

print(cnt)