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: Time Limit Exceeded)

import numpy as np
n=int(input())
s=[a for a in input()]
x = []
for a in s:
    if a == '.':
        x.append(0)
    else:
        x.append(1)
s = np.array(x)
ans = np.zeros(n).astype(np.uint8)
cnt = np.sum(s != ans)
for i in range(n):
    ans[-1 * (i+1)] = 1
    _cnt = np.sum(s != ans)
    if cnt > _cnt:
        cnt = _cnt
print(cnt)