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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>                           
#include <string>                             
using namespace std;                          
int main(void){                               
  int N,n,count = 0;                          
  int bcount = 0,wcount = 0;                  
  int now;                                    
  string s;                                   
  cin >> N;                                   
  cin >> s;                                   
  n = s.size();                               
  for(int i = 0; i < n;++i){                  
    //黒                                       
    if(s[i] == '#'){                          
      bcount++;                               
      if(i+1 < n && s[i+1] == '.'){           
        now = i;                              
        while(s[now+1] == '.'){               
          wcount++;                           
          now++;                              
        }                                     
        if(bcount >= wcount){                 
          for(int j = 1; j <= wcount;++j){    
            s[i + j] = '#';                   
          }                                   
          count += wcount;                    
        }                                     
        else if(bcount < wcount){             
          for(int j = 0; j < bcount;++j){     
            s[i - j] = '.';                   
          }                                   
          count += bcount;                    
          bcount = 0;                         
        }                                     
        wcount = 0;                           
      }                                       
    }                                         
  }                                           
  cout << count << endl;                      
  return 0;                                   
}