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: Runtime Error)

n = int(input())
s = input()
#white
i=0
numw=0
while s[i]==".":
    numw+=1
    i+=1
    if i == n:
        break
#  ..##.#..
w = s.count(".")
answ = w-numw

#black
j=-1
numb=0
while s[j]=="#":
    numb+=1
    j-=1
    if j*(-1) == n:
        break
b = s.count('#')
ansb=b-numb

#b&w
bw=0
k=numw
if k!=0:
    while s[k]=="#":
        k+=1
        bw+=1
        if k==n:
            break
wb=0
l=numb*(-1)-1
if l!=-1:
    while s[l]==".":
        l-=1
        wb+=1
        if l==n*(-1):
            break
ans3=bw+wb
print(min(ansb,answ,ans3))