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())

ans = N+1
prev = ""


black = 0
white = S.count(".")

first_white = white
first_black = N - first_white

for i in range(N):
    current = S[i]

    if prev is "#" and current is ".":

        ans = min(N, black+white)

    if current is ".":
        white -= 1
    elif current is "#":
        black += 1

    prev = current

if ans == N + 1:
    ans = 0

print(min(ans, first_black, first_white))