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()

wh = [0] * (N+1)
bl = [0] * (N+1)

for i in range(N):
    if S[i] == "#":
        bl[i+1] = bl[i] + 1
    else:
        bl[i+1] = bl[i]
        
    if S[N-1-i] == ".":
        wh[N-1-i] = wh[N-i] + 1
    else:
        wh[N-1-i] = wh[N-i]
        


ans = 1145141919810

for i in range(N+1):
    if bl[i] + wh[i] < ans:
        ans = bl[i] + wh[i]
        
print(ans)