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 MI(): return map(int, input().split())
def II(): return int(input())
def IS(): return input()
def LI(): return list(map(int, input().split()))


n = II()
s = list(IS())
count = 0
if len(s) == 1:
    print(0)
    exit()
for i in range(len(s)):
    if i == 0 and s[i] == '#' and s[i+1] == '.':
        s[i] = '.'
        count += 1
    elif i == len(s)-1:
        break
    elif s[i-1] == '.' and s[i] == '#' and s[i+1] == '.':
        count += 1
        s[i] = '.'
    elif s[i-1] == '#' and s[i] == '#' and s[i+1] == '.':
        count += 1
        s[i+1] == '#'
print(count)