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 (3.4.3) (judge verdict: Wrong Answer)

import numpy as np

n = int(input())
s = [int(i=='#') for i in input()]

idxs = [i for i, x in enumerate(s)
       if x==1]

if len(idxs)==0 or len(idxs)==n:
  print(0)
  
else:  
  s = np.array(s)
  ans = [len(idxs)]
  prev_idx = -2

  for i, idx in enumerate(idxs):
    diff = idx - prev_idx
    prev_idx = idx
    if diff>1:    
      whites = np.sum(s[idx+1:]==0)
      ans.append(i + whites)
      print(i, idx)

      if whites==0:
        break
        
  print(np.min(ans))