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)

N = int(input())
S = input()

cb = 0
cw = 0

i = 0
while i < N-1:
    idx = i
    if S[i] == '#' and S[i+1] == '.':
        cb += 1
        i += 1
        j = 1
        while True:
            if idx + j + 1 < N and S[idx +1 +  j] == '.':
                j += 1
                cb += 1
                i += 1
            else:
                break
    i += 1
        
                
i = N-2
while i >= 0:
    idx = i
    if S[i] == '#' and S[i+1] == '.':
        cw += 1
        i -= 1
        j = 1
        while True:
            if idx - j >= 0 and S[idx - j] == '#':
                j += 1
                cw += 1
                i -= 1
            else:
                break
    i -= 1
print(min(cb,cw))