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)

use std::cmp::{min,max};
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $($r)*}
    };
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}

macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}

macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}
use std::collections::VecDeque;
fn main(){
    input!{
        n:i64,
        s:chars,
    }
    let mut s = s;
    s.dedup();
    let mut black:i64 = s.iter().filter(|&c| *c=='#').count() as i64;
    let mut white = n - black;
    // let mut flag = false;
    // let mut sub = false;
    // let mut count = 0;
    // let mut white = 0;
    
    // for j in 0..n {

    //     if flag {
    //         if s[j as usize] == '.' {
    //             white += 1;
    //         }
    //         if s[(j-1) as usize] == '#' && s[j as usize] == '#'{
    //             count += 1;
    //             sub = true;
    //         } else {
    //             count = 0;
    //             sub = false;
    //         }
    //     }
    //     if s[j as usize] == '#' && !flag{
    //         flag = true;
    //     }
        
    // }
    // if sub{
    //     black -= count;
    // }
    // if s[(n-1) as usize] == '#' {
    //     black -= 1;    
    // }


    let ans = min(white,black);
    println!("{}",ans);
}