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 <bits/stdc++.h>
using namespace std;
int main(){
  int n;
  string s;
  cin>>n>>s;
  int f=0,b,c=0;
  for(int i=0;i<n;++i){
    if(s[i]=='#'&&f==0){
      f=1;
    }
    if(f==1&&s[i]=='.'){
      c++;
    }
  }
  reverse(s.begin(),s.end());
  f=0;
  int d=0;
  for(int i=0;i<n;++i){
    if(s[i]=='.'&&f==0){
      f=1;
    }
    if(f==1&&s[i]=='#'){
      d++;
    }
  }
  f=0;
  int e=0;
  for(int i=0;i<n;++i){
    if(f==0&&s[i]=='.'){
      e++;
    }
    if(s[i]=='.'&&f==0){
      f=1;
    }
    if(f==1&&s[i]=='.'){
      f=2;
    }
    if(f==2&&s[i]=='#'){
      e++;
    }

  }
  int m=min(c,d);
  m=min(m,e);
  cout<<m;
  return 0;
}