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;


fn read_line() -> String {
    let mut line = String::new();

    io::stdin().read_line(&mut line)
        .expect("Failed to read line");
    return line;
}
fn to_i(s: &str) -> i64 {
    return s.trim().parse()
        .expect("Please type a number!");
}
fn read_nums() -> Vec<i64>
{
    let line = read_line();
    let items: Vec<&str> = line.split(' ').collect();

    let mut nums: Vec<i64> = Vec::new();

    for item in items {
        nums.push(to_i(item));
    }
    return nums;
}

fn calc(n: i64, s: &Vec<char>,  flag: bool) -> i64 {
    let mut count = 0;
    let mut prev = flag;
    for i in 0..n {
        let c  = s[i as usize];
        if i == 0 {
            if c == '#' {
                if flag {
                    prev = true;
                }else {
                    prev = false;
                    count += 1;
                }
            } else {
                if flag {
                    prev = true;
                    count += 1;
                }else {
                    prev = false;
                }
            }
        } else {
            if c == '#' {
                if prev {
                    prev = true;
                } else {
                    prev = false;
                }
            } else {
                if prev {
                    prev = true;
                    count += 1;
                } else {
                    prev = false;
                }
            }
        }
        
        
    }
    count
}
fn main() {
    let n: i64 = to_i( &read_line() );
    let s: Vec<char> = read_line().chars().collect();

    let c1 = calc(n, &s, false);
    let c2 = calc(n, &s, true);

    let mut ret = 0;
    if c1<c2 {
        ret = c1;
    } else {
        ret = c2;
    }

    print!("{}", ret);
}