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)

#include <stdio.h>
#include <string.h>
#include <stdint.h>

int getNumsInt32(int32_t *buf, int32_t num)
{
  int32_t i;

  for (i = 0; i < num; i++) {
    if (scanf("%d", &buf[i]) == EOF) {
      return -1;
    }
  }
  return 0;
}

int main()
{
  int32_t num, i, change = 0;
  char s[200000];

  if (getNumsInt32((int32_t *)&num, (int32_t)1) == -1) {
    return -1;
  }

  if (scanf("%s", s) == EOF) {
    return -1;
  }

  for (i = 0; i <= num - 3; ) {
    if (s[i] == '#' && s[i + 1] == '#' && s[i + 2] == '#') {
      i += 3;
    }
    else if (s[i] == '#' && s[i + 1] == '#' && s[i + 2] == '.') {
      s[i + 2] = '#';
      change++;
      i += 2;
    }
    else if (s[i] == '#' && s[i + 1] == '.' && s[i + 2] == '#') {
      s[i] = '.';
      change++;
      i += 2;
    }
    else if (s[i] == '.' && s[i + 1] == '#' && s[i + 2] == '#') {
      i += 2;
    }
    else if (s[i] == '#' && s[i + 1] == '.' && s[i + 2] == '.') {
      s[i] = '.';
      change++;
      i += 3;
    }
    else if (s[i] == '.' && s[i + 1] == '#' && s[i + 2] == '.') {
      s[i + 1] = '.';
      change++;
      i += 3;
    }
    else if (s[i] == '.' && s[i + 1] == '.' && s[i + 2] == '#') {
      i += 2;
    }
    else if (s[i] == '.' && s[i + 1] == '.' && s[i + 2] == '.') {
      i += 3;
    }
  }

  if (i < num -1) {
    if (s[i] == '#' && s[i + 1] == '.') {
      s[i + 1] = '#';
      change++;
    }
  }

  printf("%d\n", change);

  return 0;
}