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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
public class Tenka1Begginer2019C {
    public static void Main() {
        int N = int.Parse(System.Console.ReadLine());
        string S = System.Console.ReadLine();

        int white = 0, black = 0;
        bool wStart = S[0] == '.', bEnd = S[0] == '#';
        for(int i = 0; i < N; i++) {
            if (i == N - 1) {
                if (S[i] == '#') {
                    continue;
                }
            }
            if (S[i] == '.') {
                if (wStart) {

                } else {
                    black++;
                }
            }
            if (S[i] == '#') {
                wStart = false;
                white++;
            }
        }

        if (white < black) System.Console.WriteLine(white);
        else System.Console.WriteLine(black);
    }
}