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: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Tenka1
{
    class A
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            string S = Console.ReadLine();

            int[] cw = new int[N+1]; 
            int[] cb = new int[N+1];
            int counterW = 0, counterB = 0;

            for (int i = 0; i < N; i++)
            {
                if (S[i] == '#') counterB++;
                cb[i + 1] = counterB;
                if (S[N - i - 1] == '.') counterW++;
                cw[N - i - 1] = counterW;
            }

            int min = int.MaxValue;
            for(int i = 0; i < N+1; i++)
            {
                int m = cb[i] + cw[i];
                if (m < min) min = m;
            }


            Console.WriteLine(min);
        }
    }
}