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)

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

black = 0
black_counts = [0]*N
white = 0
white_counts = [0]*N
for i in range(N):
    if S[i] == '#':
        black += 1
    black_counts[i] = black

    if S[-1-i] == '.':
        white += 1
    white_counts[N-1-i] = white

min_count = min(black_counts[N-1], white_counts[0])
for i in range(N-1):
    min_count = min(min_count, black_counts[i] + white_counts[i+1])
print(min_count)