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: Accepted)

n=int(input())
s=input()+'?'
ans=10**10
arr=[0]*n
ans1=n-s.count('#')
ans2=n-s.count('.')
if s[0]=='.':
  arr[0]=1
for i in range(1,n):
  if s[i]=='.':
    arr[i]=arr[i-1]+1
  else:
    arr[i]=arr[i-1]
for i in range(1,n):
  tmp=(i-arr[i-1])+(arr[-1]-arr[i])
  if tmp<ans:
    ans=tmp
print(min(ans,ans1,ans2))