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 std::io::*;
use std::str::FromStr;

//https://qiita.com/tubo28/items/e6076e9040da57368845
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

fn main() {
    let n: usize = read();
    let s: Vec<char> = read::<String>().chars().collect();

    //累積和の準備
    let mut whsum = vec![0; n + 1];
    let mut blsum = vec![0; n + 1];
    for i in 0..n {
        match s[i] {
            '.' => {
                whsum[i + 1] = whsum[i] + 1;
                blsum[i + 1] = blsum[i];
            }
            '#' => {
                whsum[i + 1] = whsum[i];
                blsum[i + 1] = blsum[i] + 1;
            }
            _ => {}
        }
    }

    let mut ret: u64 = std::u64::MAX;
    for left in 0..=n {
        let mut tmp: u64 = 0;
        // left の黒を白に変える
        tmp += blsum[left] - blsum[0];
        // right の白を黒に変える
        tmp += whsum[n] - whsum[left];

        ret = std::cmp::min(tmp, ret);
    }
    println!("{}", ret);
}