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: Wrong Answer)

def indexOfLeftWhite(S) :
    for i in range(len(S)):
        if (S[i] == ".") :
            return i
    return -1

def indexOfLeftBlack(S) :
    for i in range(len(S)):
        if (S[i] == "#") :
            return i
    return -1

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

counter = 0

if (S[-2:] == "#.") :
    S = S[:-1] + "#" 
    counter += 1

if (N <= 2) :
    print(counter)
else:
    for i in range(1,len(S))[::-1] :
        if (S[i-1:i+2] == "#.#") :
            S = S[:i-1] + "###" + S[i+2:]
            counter += 1
        elif (S[i-1:i+2] == "#..") :
            S = S[:i-1] + "..." + S[i+2:]
            counter += 1

print(counter)