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>
#include <algorithm>
using namespace std;

int main(){
  int n;
  string s;
  cin >> n;
  cin >> s;
  int zn=0,fn=0,endf=0;
  bool fl = true;
  for (int i=0; i < n; i++){
    if (fl && s[i]=='#'){
      fl = false;
      fn += 1;
    }else if (!fl && s[i] == '.'){
      zn += 1;
    }else if (!fl && s[i] == '#'){
      fn += 1;
    }
  }
  fl = true;
  for (int i=n-1; i >= 0; i--){
    if (fl && s[i]=='#'){
      endf += 1;
      fl = false;
    }
  }
  cout << min(zn,fn-endf);
}