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<algorithm>
char s[200001];
using namespace std;

int main(void) {
  int n;
  cin >> n;
  cin >> s;
  bool cnt_mode = false;
  int white = 0, blk = 0;
  for (int i = 0; i < n; i++) {
    if (s[i] == '#') {
      cnt_mode = true;
    }
    if (cnt_mode && s[i] == '.') {
      white++;
    }
  }
  cnt_mode = false;
  for (int i = n-1; i >= 0; i--) {
    if (s[i] == '.') {
      cnt_mode = true;
    }
    if (cnt_mode && s[i] == '#') {
      blk++;
    }
  }
  cout << min(blk, white) << endl;
  return 0;
}