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 Rust (1.42.0) (judge verdict: Accepted)

use proconio::{input, marker::Chars};

fn main() {
    input! {
        n: usize,
        s: Chars,
    }

    let mut count_white = vec![];
    let mut count_black = vec![];
    for &c in s.iter() {
        let a = if c == '#' { 1 } else { 0 };
        if let Some(&last) = count_black.last() {
            count_black.push(last + a);
        } else {
            count_black.push(a);
        }
    }
    for &c in s.iter() {
        let a = if c == '.' { 1 } else { 0 };
        if let Some(&last) = count_white.last() {
            count_white.push(last + a);
        } else {
            count_white.push(a);
        }
    }
    let num_white = *count_white.last().unwrap();
    for e in count_white.iter_mut() {
        *e = num_white - *e;
    }

    let mut ans = n;
    for i in 0..=n {
        let mut temp = 0;
        if i > 0 {
            temp += count_black[i - 1];
        }
        if i < n {
            temp += count_white[i];
        }

        ans = std::cmp::min(ans, temp);
    }

    println!("{}", ans);
}