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 (1.15.1) (judge verdict: Wrong Answer)

fn main() {
    let _: u32 = read();
    let s: String = read();

    let cs = s.chars().collect::<Vec<char>>();

    let mut flag = false;
    let mut counter: u64 = 0;

    for c in cs.clone() {
        // # が出るまで送る
        match (flag, c) {
            (false, '.') => { continue; },
            (false, '#') => { flag = true; },
            (true, '.') => {counter += 1;}
            _ => {}
        }
    }

    flag = false;
    let mut counter2: u64 = 0;
    for c in cs.iter().rev() {
        // . が出るまで送る
        match (flag, c) {
            (false, &'#') => { continue; },
            (false, &'.') => { flag = true; },
            (true, &'#') => {counter2 += 1;}
            _ => {}
        }
    }

    println!("{}", 
        if counter > counter2 {
            counter2
        } else {
            counter
        }
    );

}

#[warn(dead_code)]
fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

#[warn(dead_code)]
fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().split_whitespace()
        .map(|e| e.parse().ok().unwrap()).collect()
}

#[warn(dead_code)]
fn read_mat<T: std::str::FromStr>(row: u32) -> Vec<Vec<T>> {
    let mut vec = Vec::new();

    for _i in 0..row {
        vec.push(read_vec::<T>());
    }

    vec
}