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)

N = int(input())
S = input()
s = S.replace('.#', '.0#').replace('#.', '#0.').split('0')

m = len(s)
p0 = s[0]
p1 = False
ans = 0

for i in range(1, m):
    if not p1:
        if i >= m - 1 and s[i][0] == '#':continue
        if i >= m - 1 and s[i][0] == '.':
            ans += min(len(s[i]), len(p0))
        p1 = s[i]
        continue
    if p0[0] == '#' and p1[0] == '.' and s[i][0] == '#':
        if len(p0) > len(p1):
            ans += len(p1)
            p0 = '#' * (len(p0) + len(p1) + len(s[i]))
            p1 = False
        else:
            ans += len(p0)
            p0 = '.' * (len(p0) + len(p1))
            p1 = s[i]
    elif p0[0] == '.' and p1[0] == '#' and s[i][0] == '.':
        if len(p1) >= len(s[i]):
            ans += len(s[i])
            p1 = '#' * (len(p1) + len(s[i]))
        else:
            ans += len(p1)
            p0 = '.' * (len(p0) + len(p1) + len(s[i]))
            p1 = False
        
print(ans)