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 search_left_white(int r, int l, int n, string S);
int search_right_black(int r, int l, int n, string S);


int main()
{
    int N;
    string S;

    cin >> N;
    cin >> S;

    int left = 0;
    int right = N -1;

    for(int i=0; i<N; i++){
        if(S[i] == '#'){
            left = i;
            break;
        }
    }

    for(int i=N-1; i>=0; i--){
        if(S[i] == '.'){
            right = i;
            break;
        }
    }

    if(left == 0 || right == (N-1)){
        cout << 0 << endl;
        return 0;
    }

    int min = N;

    for(int i=left; i<=right; i++){
        int count = 0;
        
        count += search_left_white(left, right, i, S);
        count += search_right_black(left, right, i, S);

        if(count < min){
            min = count;
        }
    }

    cout << min << endl;

    return 0;
}

int search_left_white(int r, int l, int n, string S)
{
    int count = 0;

    for(int i=r; i<n; i++){
        if(S[i] == '#'){
            count++;
        }
    }

    return count;   
}

int search_right_black(int r, int l, int n, string S)
{
    int count = 0;

    for(int i=l; i>=n; i--){
        if(S[i] == '.'){
            count++;
        }
    }

    return count;
}