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)

# -*- coding: utf-8 -*-
import sys
# ----------------------------------------------------------------
# Use Solve Function

def solve(lines):
    N = int(lines.pop(0))
    S = lines.pop(0)
    # reverse
    S = S[::-1]
    # 白が現れるまで省く
    idx = S.find('.')
    S = S[idx:]

    res = 0
    while(True):
        w = S.find('#')
        b = S[w:].find('.')

        if w < 0:
            break

        if ( w < b ):
            res += w
            S = S[w+b:]
        else:
            res += min(S.count('.'), S.count('#'))
            break

    print(res)

lines = [x.strip() for x in sys.stdin.readlines()]

#
# solve !!
#
solve(lines)