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 = str(input())
# '.'の場合は白, '#'の場合は黒

if S[0] == '.':
    count_white = [1]
    count_black = [0]
else:
    count_white = [0]
    count_black = [1]


for i in range(1, N):
    if S[i] == '.':
        # 見ている石が白なら
        count_white.append(count_white[i-1]+1)
        count_black.append(count_black[i-1])
    else:
        # 見ている石が黒なら
        count_white.append(count_white[i-1])
        count_black.append(count_black[i-1]+1)

tmp = 0
for i in range(1, N):
    min_sum = 0
    min_sum += count_black[i-1]
    min_sum += (count_white[N-1] - count_white[i])
    tmp = min(tmp, min_sum)

print(tmp)