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: Accepted)

#[allow(unused_macros)]
macro_rules! p {
    ($x:expr $(, $tail:expr)*) => {
        let mut s = String::new();
        s.push_str(format!("{:?}", $x).as_str());
        $(
            s.push_str(format!(", {:?}", $tail).as_str());
        )*
        println!("{}", s);
    };
}

#[allow(unused_macros)]
macro_rules! pl {
    ($($x:expr), *) => {
        $(println!("{:?}", $x);)*
    };
}

macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! stdin {
    () => {{
        use std::io::Read;
        let mut s = String::new();
        std::io::stdin().read_to_string(&mut s).unwrap();
        s
    }};
}

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

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

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

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

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

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

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

fn main() {
    println!("{}", solve(stdin!()));
}

fn solve(src: String) -> String {
    input! {
        source = src,
        n: usize,
        s: chars,
    }
    let mut white = 0;
    for i in 0..n {
        if s[i] == '.' {
            white += 1;
        }
    }
    let mut left_black = 0;
    let mut right_white = white;
    let mut ans = right_white;
    for i in 0..n {
        if s[i] == '#' {
            left_black += 1;
        } else if s[i] == '.' {
            right_white -= 1;
        }
        ans = std::cmp::min(ans, left_black + right_white);
    }
    ans.to_string()
}

// Test Code

macro_rules! test {
    ($($input:expr => $output:expr),* $(,)*) => {
        #[test]
        fn solve_test() {
            $(
                assert_eq!(solve($input.to_string()), $output);
            )*
        }
    };
}

test! {
r"
3
#.#
" => "1",

r"
5
#.##.
" => "2",

r"
9
.........
" => "0",

r"
9
##...#.#.
" => "4",
}