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: Runtime Error)

use std::iter::*;
use std::cmp::*;

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn print<T: std::fmt::Display>(x: T) -> () {
    println!("{}", x);
}


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

    let mut cs1 = cs.clone();
    let mut ans1 = 0;
    for i in 0..(n - 2) {
        if cs1[i] == '#' && cs1[i + 1] == '.' {
            if cs1[i + 2] == '.' {
                cs1[i] = '.';
                ans1 += 1;
            } else {
                cs1[i + 1] = '#';
                ans1 += 1;
            }
        }
    }

    if cs1[n - 2] == '#' && cs1[n  - 1] == '.' {
        ans1 += 1;
    }


    let mut ans2 = 0;
    let mut cs2 = cs.clone();
    cs2.reverse();
    for i in 0..(n - 2) {
        if cs2[i] == '.' && cs2[i + 1] == '#' {
            if cs2[i + 2] == '#' {
                cs2[i] = '#';
                ans2 += 1;
            } else {
                cs2[i + 1] = '.';
                ans2 += 1;
            }
        }
    }

    if cs2[n - 2] == '.' && cs2[n  - 1] == '#' {
        ans2 += 1;
    }

    let ans: usize = min(ans1, ans2);
    print(ans);
}