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 PyPy3 (2.4.0) (judge verdict: Accepted)

def main():
    N = int(input())
    S = input()
    black = [0] * (N+1)
    white = [0] * (N+1)
    for i in range(N):
        black[i+1] = black[i]
        white[N-i-1] = white[N-i]
        if S[i] == "#":
            black[i+1] += 1
        if S[N-i-1] == ".":
            white[N-i-1] += 1
    ans = float("inf")
    for i in range(N+1):
        ans = min(ans, black[i] + white[i])
    print(ans)


if __name__ == "__main__":
    main()