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 PyPy3 (2.4.0) (judge verdict: Wrong Answer)

n = int(input())
s = input()

def count_diff(str1, str2):
  return sum([1 if j == str2[i] else 0 for i, j in enumerate(str1)])

if '.' not in s or '#' not in s:
  print(0)
elif '#.' not in s:
  print(0)
else:
  if s[n-1] == '#':
    s = s[:s.rfind('.')+1]
  if '#' in s:
    s = s[s.find('#'):]
  len_s = len(s)
  q = ['.' * i + '#' * (len_s - i) for i in range(0, len_s+1)]
  print(min([count_diff(s, te) for te in q]))