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::Read;
use std::cmp::min;

fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();

    let answer = solve(&buf);

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

fn solve(input: &str) -> String {
    let mut iterator = input.split_whitespace();

    let n: usize = iterator.next().unwrap().parse().unwrap();
    let s: Vec<char> = iterator.next().unwrap().chars().collect();

    let mut s1 = s.clone();
    let mut c1: usize = 0;
    for i in 0..(n - 1) {
        if s1[i] == '#' && s1[i + 1] == '.' {
            s1[i + 1] = '#';
            c1 += 1;
        }
    }

    let mut s2 = s.clone();
    let mut c2: usize = 0;
    for i in (1..n).rev() {
        if s2[i - 1] == '#' && s2[i] == '.' {
            s2[i - 1] = '.';
            c2 += 1;
        }
    }

    return min(c1, c2).to_string();
}