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;
using System.Linq;
class M{static void Main(String[] _) {
  int N = int.Parse(Console.ReadLine());
  var S = Console.ReadLine();
  var s = S.ToCharArray();
  int r1 = 0;
  int r2 = 0;
  
  int T = S.Length;
  
  r1 = T;
  for( int I=0 ; I<T ; ++ I ) {
    if ( s[I] == '#' ) {
      r1 = I;
      break;
    }
  }  
	
  r2 = -1;
  for( int I=T-1 ; 0<=I ; -- I ) {
    if ( s[I] == '.' ) {
      r2 = I;
      break;
    }
  }
  
  
  int r3 = 0;
  for( int I=r1 ; I<=r2 ; ++I ) {
    if ( s[I] == '.' ) r3 ++;
  }
  
  if ( r2 - r1 > r3 ) {
    Console.WriteLine( r3 );
  } else {
    Console.WriteLine( r2 - r1 - r3 + 1 );
  }  
  
}
       
       
       
       
}