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()
i = 0
while i < N:
    if S[i] == "#":
        break
    i += 1
t_b = 0
k = N-1
while(S[k] == "#"):
    k -= 1
    t_b += 1
if i == N:
    print(0)
else:
    count = 0
    for j in range(i,N):
        if S[j] == ".":
            count += 1
    if N - (count + i) - t_b <= count:
            print(N - count - i - t_b)
    else:
            print(count)