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 = str (input ())

def dot_num ():
    cnt = 0
    for i in range (N):
        if S [i] == '.':
            cnt += 1
    return cnt

def hash_num ():
    cnt = 0
    for i in range (N):
        if S [i] == '#':
            cnt += 1
    return cnt

dots = dot_num ()
hashes = hash_num ()

if S [0] == '.' and S [1] == '#':
    dots -= 1

if S [N-1] == '#' and S [N-2] == '.':
    hashes -= 1
    
print (min (dots, hashes))