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 (2.7.6) (judge verdict: Accepted)

n=int(raw_input())
s=raw_input()

temp=s.count("#")
if temp==0 or temp==n:
    print(0)
else:
    head=0
    tail=n-temp
    ret=tail+head
    for c in s:
        if c=="#":
            head+=1
        else:
            tail-=1
        temp2=head+tail
        if temp2<ret:
            ret=temp2
    print(ret)