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 <stdio.h>
#include <iostream>
using namespace std;

int main(){
	int num;
	cin >> num;
	string stone;
	cin >> stone;
	int ans = 20000;
	int black = 0;
	int left_black = 0;
	for(int i = 0; i < num; i++){
		if(stone[i] == '#') black++;
	}

	for(int i = 0; i < num; i++){
		if(stone[i] == '#'){
			if(ans > num - i - black + 2*left_black) ans = num - i - black + 2*left_black;
			left_black++;
		}
        if(i == num -1 && ans > black){
			ans = black;
		}
	}
	cout << ans << endl;
	return 0;
}