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 n;
 char s[200000];
 int i;
 int sum=0;
 scanf("%d",&n);
 scanf("%s",&s[0]);
  for(i=0;i<n;i++){
    if(s[i]=='#'&&s[i+1]=='.'&&s[i-1]=='.'){
      s[i]='.';
      sum++;
    }
    else if(s[i]=='.'&&s[i+1]=='#'&&s[i-1]=='#'){
      s[i]='#';
      sum++;
    }
  }
 printf("%d",sum);
}