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: Accepted)

import numpy as np

N = int(input())
S = list(input())

black_stones = []
white_stones = []

black_stone_counter = 0
for stone_color in S:
    if stone_color == "#":
        black_stone_counter += 1
    black_stones.append(black_stone_counter)

white_stone_counter = 0
for stone_color in S[::-1]:
    if stone_color == ".":
        white_stone_counter += 1
    white_stones.append(white_stone_counter)

black_stones_np = np.array(black_stones)
white_stones.reverse()
white_stones_np = np.array(white_stones)

sum_stones_np = black_stones_np + white_stones_np

print(sum_stones_np.min()-1)