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)

import sys
from itertools import accumulate

def main():
    input = sys.stdin.readline
    N = int(input())
    S = [0 if c == '.' else 1 for c in input().strip()]
    T = [0] + list(accumulate(S))

    B = T[N]
    if B == 0 or B == N:
        return 0

    ans = 10**5
    for i in range(N+1):
        convert_w = T[i]
        convert_b = N - (B - T[i])
        ans = min(ans, convert_w + convert_b)

    return ans


if __name__ == '__main__':
    print(main())