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: Accepted)

#include<iostream>
#include<vector>
#include<string>
#include<stdlib.h>
using namespace std;

int main() {
	int N;
	string S;

	cin >> N;
	cin >> S;

	int count_b = 0, count_w = 0;

	for (int i = 0; i < N; i++) {
		if (S[i] == '#')
			count_b++;
		else
			count_w++;
	}

	vector<int> change(N+1, 0);

	change[0] = count_w;//変えるべき数

	for (int i = 1; i <= N; i++) {
		if (S[i-1] == '.')
			change[i] = change[i - 1] - 1;
		else
			change[i] = change[i - 1] + 1;
	}

	int min = change[0];

	for (int i = 1; i <= N; i++) {
		if (change[i] < min) {
			min = change[i];
		}
	}

	cout << min << endl;

}