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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>

int
compare_int(const void *a, const void *b)
{
    return *(int*)a - *(int*)b;
}

int
main(void)
{
        int N;
        int flag;
        int pre = 0;
        int post = 0;
        int black = 0;
        int white = 0;

        scanf("%d\n", &N);

        for (int i = 0; i < N; i++) {
                char c;
                char stone;
                scanf("%c", &c);

                if (c == '.')
                        stone = 0;
                else
                        stone = 1;

                if (stone == 1) {
                        black++;
                        if (black < white)
                                pre++;
                } else if (black > 0) {
                        white++;
                        if (pre < black)
                                post++;
                }
        }

        int temp[3] = {
                white, black, pre + post
        };
        qsort(temp, 4, sizeof(int), compare_int);

        printf("%d", temp[0]);

        return 0;
}