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)

N=input()
S=input()
 
# #を検出してその右にある全ての.をシャープに変える。最も左側にあるシャープを見つけてそれより右にある.の個数を返す
 
def first(S):
    if "#" in S:
        ichi=S.index("#")
        return int(S.count(".",ichi))
    else:
        return 0
 
# .を検出してその左にある＃を.に変える。最も右にある.を見つけてそれより左にある#を数える。
def second(S):
    if "." in S:
        ichi =S.rindex(".")
        return int(S.count("#",0,ichi))
    else:
        return 0
print(max([first(S),second(S)]))