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# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;

namespace C
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string s = Console.ReadLine();
            int w = 0;
            int b = 0;
            for(int i = 0; i < n; i++)
            {
                if (s[i] == '.') w++;
                if (s[i] == '#') b++;
            }
            int ans = 0;
            if (w >= b)
            {
                ans = b;
                int cnt = n-1;
                while (s[cnt] == '#')
                {
                    ans--;
                    cnt--;
                }
            }else if (w < b)
            {
                ans = w;
                int cnt = 0;
                while (s[cnt] == '.')
                {
                    ans--;
                    cnt++;
                }
            }
            Console.WriteLine(ans);
        }
    }
}