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++ (GCC 9.2.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;

int main() {
  int N;
  string S;
  cin >> N >> S;
  int count = 0;
  int A = 0;
  int B = N-1;
  
  while (B-A >= 1){
    if (S.at(A) == '#' && S.at(B) == '.'){
      if (B-A == 1){
        count++;
        cout << count << endl;
        return 0;
      }
      else {
        count += 2;
        A++;
        B--;
      }
    }
    else if (S.at(A) == '.'){
      A++;
    }
    else if (S.at(B) == '#'){
      B--;
    }
  }
  cout << count << endl;
}