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: Runtime Error)

def func(s, count):
    if len(s) > 0:
        pos1 = s.find("#")
        pos2 = s.find(".")
        pos3 = s[pos2:].find("#")
        if pos3 == -1:
            pos3 = len(s)
        else:
            pos3 = pos3+pos2
        #print(pos1, pos2, pos3, s)
        if pos1 == -1 or pos2 == -1:
            return count

        if pos2-pos1 < pos3-pos2:
            count += pos2-pos1
        else:
            count += pos3-pos2

        return func(s[pos3:], count)
    else:
        return count

if __name__ == '__main__':
    N = int(input())
    S = input()
    print(func(S, 0))