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)

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

int main(void) {
	int n,cnt1=0,cnt2=0,cnt3=0,cnt4=0,f=0;
	char s[2000000],sp[2000000];
	
	scanf("%d",&n);
	scanf("%s",&s);
	
	for(int i=0;i<n;i++)
		sp[i] = s[i];
	
	for(int i=0;i<n;i++){
		if((f==0) && s[i] == '#') f=1;
		if((f==1) && s[i] == '.') cnt1++;
	}
	
	f=0;
	
	for(int i=n-1;i>=0;i--){
		if((f==0) && s[i] == '.') f=1;
		if((f==1) && s[i] == '#') cnt2++;
	}
	
	for(int i=1;i<n-1;i++){
		if((sp[i-1] == sp[i+1]) && (sp[i-1] != sp[i])){
			sp[i] = sp[i-1];
			cnt3++;
		}
		if((i==n-2) && sp[i]=='#'){
			if(sp[i+1] == '.') cnt3++;
		}
	}
	
	for(int i=0;i<n;i++)
		sp[i] = s[i];
		
	for(int i=n-2;i>0;i--){
		if((sp[i-1] == sp[i+1]) && (sp[i-1] != sp[i])){
			sp[i] = sp[i-1];
			cnt4++;
		}
		if((i==1) && sp[i]=='.'){
			if(sp[0] == '#') cnt4++;
		}
	}
	
	if(cnt4 < cnt3) cnt3 = cnt4;
	
	if(cnt1 < cnt2){
		if(cnt1 < cnt3) printf("%d\n",cnt1);
		else printf("%d\n",cnt3);
	}
	else if(cnt2 < cnt3) printf("%d\n",cnt2);
	else printf("%d\n",cnt3);

	return 0;
}