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 math
import sys
N = int(input())
s = input()
sh = []
dot = []
num = 0
for i in s:
    if i == '#':
        num += 1
        sh.append(num)
    else:
        sh.append(num)
num = 0
for i in s:
    if i == '.':
        num += 1
        dot.append(num)
    else :
        dot.append(num)
ans = 1e9
for i in range(N):
    tmp = sh[N-1] - sh[i] + dot[i]
    ans = min(ans, tmp)
print(ans)