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)

N = int(input())
s = str(input())
S = list(s[i] for i in range(N))

test = S
countf = 0

if S == list(sorted(S)[::-1]):
    print(0)

else:
    while test != list(sorted(test)[::-1]):
        a = test.index("#")
        test[a] = "."
        countf += 1
        del test[0:a+1]
        if test == list(sorted(test)[::-1]):
            break
        test.reverse()
        b = test.index(".")
        test[b] = "#"
        countf += 1
        del test[0:b+1]
        test.reverse()

    print(countf)