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::io::stdin;
use std::time::SystemTime;

fn main() {
    let n: u64 = read().parse().unwrap();
    let mut s: Vec<char> = read().chars().collect();
    let mut s2 = s.clone();
    let mut count = 0;
    let mut count2 = 0;
    loop {
        let count1 = check2(&mut s);
        if count1 == 0 {
            break;
        }
        count = count + count1;
    }
    loop {
        let count22 = check(&mut s2);
        if count22 == 0 {
            break;
        }
        count2 = count2 + count22;
        if count2 >= count {
            break;
        }
    }
    if count < count2 {
        println!("{}", count);
    } else {
        println!("{}", count2);
    }
}

fn check(v: &mut Vec<char>) -> u64 {
    let mut count = 0;
    for i in 1..v.len() {
        if v[i] == '.' && v[i - 1] == '#' {
            v[i - 1] = '.';
            count = count + 1;
        }
    }
    count
}

fn check2(v: &mut Vec<char>) -> u64 {
    let mut count = 0;
    for i in 0..v.len()-1 {
        if v[i] == '#' && v[i + 1] == '.' {
            v[i + 1] = '#';
            count = count + 1;
        }
    }
    count
}

fn read() -> String {
    let mut s = String::new();
    stdin().read_line(&mut s).unwrap();
    s.trim().to_string()
}