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 <bitset>
#include <string>
#include <algorithm>
#include <cmath>
#include <vector>
using namespace std;

#define REP(i,n) for(int i=0;i<n;i++)

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

    long long int count = 0;
    long count_white = 0;
    long count_black = 0;
    for(int i = 0; i < S.size(); i++)
    {
        char stone_now = S[i];
        if (stone_now == '.')
        {
            count_white++;
            if (S[i+1] == '#' or i == S.size()-1) // end
            {
                
                count += min(count_black, count_white);
                
                count_black = 0;
                count_white = 0;
            }
        }
        else if (stone_now == '#')
        {
            count_black++;
        }
    }
    cout << count << endl;
}