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: Runtime Error)

#include <iostream>
#include <string>
using namespace std;

int main(){
  int N;
  cin >> N;
  string S;
  cin >> S;

  // 左側に白 右側に黒が並ぶようにする


  // 左側から交互に見ていく
  int left_out = 0;
  int flag = 1;
  int left_idx = 0;
  int right_idx = N-1;
  while(1){
    if (flag){
      if (S[left_idx] == '#'){
        left_out += 1;
        flag = 0;
      }
      left_idx += 1;
    } else{
      if (S[right_idx] == '.'){
        left_out += 1;
        flag = 1;
      }
      right_idx -= 1;
    }

    if (left_idx == right_idx){
      break;
    }
  }

  // 右側から交互に見ていく
  int right_out = 0;
  flag = 0;
  left_idx = 0;
  right_idx = N-1;
  while(1){
    if (flag){
      if (S[left_idx] == '#'){
        right_out += 1;
        flag = 0;
      }
      left_idx += 1;
    } else{
      if (S[right_idx] == '.'){
        right_out += 1;
        flag = 1;
      }
      right_idx -= 1;
    }
    if (left_idx == right_idx){
      break;
    }

  }

  if (left_out < right_out){
    cout << left_out << endl;
  } else{
    cout << right_out << endl;
  }

  return 0;
}