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

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()
}

pub fn main() {
    let N: usize = read();
    let S: String = read();
    let mut w_counter = 0;
    let mut start = false;
    for c in S.chars() {
        if c == '.' {
            if !start {
                continue;
            }
            w_counter += 1;
        } else {
            start = true;
        }
    }

    let mut b_counter = 0;
    start = false;
    for c in S.chars().rev() {
        if c == '#' {
            if !start {
                continue;
            }
            b_counter += 1;
        } else {
            start = true;
        }
    }
    println!("{}", ::std::cmp::min(w_counter, b_counter));
}