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)

import sys
N = int(sys.stdin.readline().rstrip())
S = list(sys.stdin.readline().rstrip())

if len(S) == 1:
    print(0)
    exit()

cnt_b = S.count("#")
cnt_w = N - cnt_b

ans_1 = cnt_b
ans_2 = 0
flag = False
for s in S:
    if s == ".":
        if flag:
            ans_2 += 1
    else:
        if not flag:
            flag = True
            
print(min(ans_1, ans_2))