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;
namespace C
{
    class Cmondai
    {
        static void Main()
        {
            int n = int.Parse(Console.ReadLine());
            String s = Console.ReadLine();
            int dst;
            int tdst = 0;
            for(int j=0;j<n;j++){
                if(s[j]=='.'){
                    tdst ++;
                }
            }
            dst = tdst;
            for(int i=0;i<n;i++){
                if(s[i]=='.'){
                    tdst --;
                }
                else{
                    tdst ++;
                }
                if(tdst<dst){
                    dst = tdst;
                }
            }
            Console.WriteLine(dst.ToString());
        }
    }
}