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>
int main(void)
{
  int a;
  int N;
  char stone[200000];
  int result=0;
  
  scanf("%d",&N);
  scanf("%s",stone);
  
  for(a=0;a<N-2;a++){
    if(stone[a] == '#')//黒
    {
      if(stone[a+1] == '#')//黒黒
      {
        if(stone[a+2] == '.' && a == N-3)
        {
          stone[a+2] ='.';
          result++;
        }
      }
        
      else if(stone[a+1] == '.')//黒白
      {
        if(stone[a+2] == '#')//黒白黒
        {
          stone[a+1] = '#';
          result++;
        }
        else if(stone[a+2] == '.')//黒白白
        {
          stone[a] ='.';
          result++;
        }
      }
    }
  }

  printf("%d",result);
  return 0;
}