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 (GCC 5.4.1) (judge verdict: Wrong Answer)

/*
 * main.c
 *
 *  Created on: 2019/04/20
 *      Author: family
 */

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

char S[2*100001] = {0};

int main()
{
    int N;
    int i = 0;
    int black = 0, white = 0;
    int ans = 0;
    scanf("%d", &N);
    scanf("%s", S);
    for(i = (N-1); 0 <= i ; i--) {
        if(S[i] == '#') {
            black++;
        } else {
            white++;
            if(black != 0) {
                if(white > black) {
                    ans += black;
                } else {
                    ans += white;
                }
                black = 0;
                white = 0;
            }
        }
    }
    if((black != 0) && (white > black)) {
        ans += black;
    } else {
        ans += white;
    }
    printf("%d\n",ans);
    return 0;
}