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>
using namespace std;

int n;
string s;
int c = 0;

void changeBlack(){
  for (int i = 0; i < n - 1; i++){
    if (s[i] == '#' && s[i+1] == '.'){
      s[i] = '.';
      c += 1;
    }
  }
}

void changeWhite(){
  for (int i = n; i > 0; i--){
    if (s[i] == '.' && s[i-1] == '#'){
      s[i] = '#';
      c += 1;
    }
  }
}

int main(){
  cin >> n >> s;

  int bnum = 0;
  int wnum = 0;

  for(int i = 0; i < n; i++){
    if(s[i] == '#'){
      bnum += 1;
    }else{
      wnum += 1;
    }
  }
  if (bnum > wnum){
    changeBlack();
  }else{
    changeWhite();
  }

  cout << c << endl;
  return 0;
}