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()

black_start = s.find("#")
black_end = s.rfind("#")

white_start = s[black_start:].find(".")
white_end = s[black_start:].rfind(".")

black = s[black_start:].count("#")
white = s[black_start:].count(".")

if black == 0 or white ==0:
    print(0)
else:
    if (white_end - white_start +1) == s[white_start:white_end+1].count(".") and white_end < black_end :
        print(1)
    else:
        print(min(black, white))