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())
stone_list = list(input())
stone_list.append('end')
if stone_list[0] == '#':
    stone_list.insert(0,'.')

normalized_list = []
count = 0
stone = stone_list[0]
for s in stone_list:
    if s == stone:
        count += 1
    else:
        normalized_list.append(count)
        count = 1
        stone = s
    

total_a = 0
for i in range(1,len(normalized_list)-1,2):
    total_a += normalized_list[i]
    
total_b = 0
for i in range(2,len(normalized_list),2):
    total_b += normalized_list[i]

print(min(total_a,total_b))