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>
#include <iostream>
#include <cstring>
#include <cmath>
#include <unistd.h>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#define PI 3.14159265358979323846
 
using namespace std;
 
int main()
{
	ios_base::sync_with_stdio(false);
	int N, pe=0, be=0, pd, bd, min=100010;
	char S[200010], aux;
 
	cin >> N;
	cin.ignore();
	for(int i=0;i<N;i++)
	{
		cin >> aux;
		S[i]=aux;
		if(aux=='#')
			pd++;
		else
			bd++;
	}

	if(pe+bd<min)
		min = pe+bd;

	for(int i=0;i<N;i++)
	{
		if(S[i]=='#')
		{
			pd--;
			pe++;
		}
		else
		{
			bd--;
			be++;
		}

		if(pe+bd<min)
			min = pe+bd;
	}

	cout << min << endl;
 
	return 0;
}