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>

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

	int count=0; int bcount=0; int wcount=0;
	for (int i = 1; i < n-1; ++i)
	{
		if(s[i-1]=='#'&&s[i]=='.'&&s[i+1]=='.'){
			wcount++;
			count++;
		}
		if(count==1&&s[i-1]=='.'&&s[i]=='.'&&s[i+1]=='.'){
			wcount++;
		}
		if(s[i-1]=='.'&&s[i]=='.'&&s[i+1]=='#'){
			count=0;
		}

		if(s[i-1]=='.'&&s[i]=='#'&&s[i+1]=='#'){
			bcount++;
			count++;
		}
		if(count==1&&s[i-1]=='#'&&s[i]=='#'&&s[i+1]=='#'){
			bcount++;
		}
		if(s[i-1]=='#'&&s[i]=='#'&&s[i+1]=='.'){
			count=0;
		}
	}

	if(bcount>=wcount) printf("%d",ans+wcount);
	else printf("%d",ans+bcount);
	return 0;
}