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)

#![allow(unused, non_snake_case, dead_code, non_upper_case_globals)]
use {
    proconio::{marker::*, *},
    std::{cmp::*, collections::*, mem::*},
};
fn main() {
    input! {//
        n:usize,
        s:Chars,
    }
    let mut rwhite = s.iter().filter(|&&x| x == '.').count() as i64;
    let mut rblack = s.iter().filter(|&&x| x == '#').count() as i64;

    let mut lwhite = 0;
    let mut lblack = 0;
    let mut ans = rwhite;
    const INF: i64 = 1 << 60;
    for (i, &c) in s.iter().enumerate() {
        if c == '.' {
            lwhite += 1;
            rwhite -= 1;
        } else {
            lblack += 1;
            rblack -= 1;
        }
        ans = min(lblack + rwhite, ans);
    }
    println!("{}", ans);
}