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()
 
if s.count('.') == len(s):
    print(0)
else:
    s_ = s
    for i, wb in enumerate(s_):
        if wb == '.':
            s_ = s[i+1:]
        else:
            break
    
    ans_black_change = s_.count('#')
    if s[-1] == '#':
        ans_black_change -= 1
    ans_white_change = s_.count('.')
    
    ans = min(ans_black_change, ans_white_change)
    print(ans)