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 <string.h>

//白黒にする
//.....####みたいにする
//.白. #黒#

int main(void)
{
	
	int n;
	int num[300000] = {0};
	int index = 0;
	int index_kuro;
	int index_siro;
	int count;
	int i, j;
	char str[300000];
	
	scanf("%d%s", &n, str);
	
	str[n] = 'a';
	
	count = 0;
	if(str[0] == '#') {
		num[0] = 0;
		index++;
	}
	
	for(i = 0; i <= n; i++) {
		if(str[i] == '.') {
			count = 1;
			for(j = i + 1; j <= n; j++) {
				if(str[j] != '.') {
					break;
				}
				count++;
			}
			i = j - 1;
			num[index] = count;
			index++;
		} else if(str[i] == '#') {
			count = 1;
			for(j = i + 1; j <= n; j++) {
				if(str[j] != '#') {
					break;
				}
				count++;
			}
			i = j - 1;
			num[index] = count;
			index++;
		}
	}
	
	count = 0;
	index_kuro = 1;
	if(index <= 2) {
		printf("0\n");
		return 0;
	}
	if(index % 2 == 0) {
		index_siro = index - 2;
	} else {
		index_siro = index - 1;
	}
	
	while(index_kuro < index_siro) {
		if(num[index_kuro] > num[index_siro]) {
			count += num[index_siro];
			index_siro -= 2;
		} else {
			count += num[index_kuro];
			index_kuro += 2;
		}
	}
	
	printf("%d\n", count);
	
	return 0;
}