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)

def main():
    n = int(input())
    s = input().rstrip()
    i = 0
    b_count = 0
    w_count = 0
    # Comsume left whites
    while i < len(s):
        if s[i] == '.':
            i += 1
        else:
            break

    #Consume right blacks
    j = len(s) - 1
    while j > i:
        if s[j] != '.':
            j -= 1
        else:
            break

    while i <= j:
        if s[i] == '.':
            i += 1
            w_count += 1
        else:
            i += 1
            b_count += 1

    print(min(w_count, b_count))

if __name__ == "__main__":
    main()