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! invec {
    ( $t:ty ) => {{
        let mut s = String::new();
        match std::io::stdin().read_line(&mut s) {
            Ok(0) => Vec::<$t>::new(),
            Ok(n) => s.trim().split_whitespace().map(|s| s.parse::<$t>().unwrap()).collect::<Vec<$t>>(),
            Err(_) => Vec::<$t>::new(),
        }
    }}
}

#[allow(unused_macros)]
macro_rules! input {
    ( $($t:ty),* ) => {{
        let mut s = String::new();
        std::io::stdin().read_line(&mut s);
        let mut splits = s.trim().split_whitespace();
        ($(
            {
                 splits.next().unwrap().parse::<$t>().unwrap()
            },
        )*)
    }}
}

#[allow(unused_must_use)]
#[allow(unused_variables)]
fn solve() {
    let (n, ) = input!(usize);
    let (s, ) = input!(String);

    let mut accum_whites = vec![];
    let mut accum_blacks = vec![];

    let mut whites = 0;
    let mut blacks = 0;

    accum_blacks.push(0);
    accum_whites.push(0);
    for (i, c) in s.char_indices() {
        if c == '.' {
            whites += 1;
        } else {
            blacks += 1;
        }

        accum_blacks.push(blacks);
        accum_whites.push(whites);
    }

    let mut min = std::u32::MAX;

    for i in 0..(n+1) {
        let reverse = accum_blacks[i] - accum_blacks[0] + accum_whites[n] - accum_whites[i];
        min = std::cmp::min(min, reverse);
    }

    println!("{}", min);
}

fn main() {
    solve();
}