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)

from itertools import groupby
N = int(input())
s = groupby(list(input()))
table = []
for key,group in s:
  cnt = 0
  for id,_ in enumerate(group,1):
    cnt = id
  table.append([key,cnt])
#print(table)
if len(table) == 1:
  print(0)
  exit()
if table[0][0] == ".":
  table = table[1:]
ans = 0
for t in table:
  if t[0] == ".":
    ans += t[1]
print(ans)