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()
cnt_b = 0
cnt_w = 0
Is_Black = False
ans = 0

# ans = S.count("#.")
# print(ans)

for i in range(N):
    if S[i] == "#":
        if Is_Black:
            if cnt_w == 0:
                cnt_b += 1
            elif cnt_b != 0 and cnt_w != 0:
                ans += min(cnt_b, cnt_w)
                cnt_b = 1
                cnt_w = 0
        else:
            Is_Black = True
            cnt_b += 1
    else:
        if Is_Black and cnt_b!=0:
            cnt_w += 1
else:
    if cnt_b != 0 and cnt_w != 0:
                ans += min(cnt_b, cnt_w)
                cnt_b = 1
                cnt_w = 0

print(ans)