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>
char s[2000001];
int main(void){
	int n;
	scanf("%d",&n);
	scanf("%s",s);
	int i;
	int ans = 0,white = 0,black=0;
	int wn = 0,bn = 0;
	//まず左から連続する白の個数を数える
	i = 0;
	while(s[i]=='.'){
		white++;
		i++;
	}
	//右から連続する黒の個数を数える
	i = n-1;
	while(s[i]=='#'){
		black++;
		i--;
	}
	//あとはそれ以外を白か黒に塗りつぶす場合の手数を考える。
	for(i=white;i<n-black;i++){
		if(s[i]=='.')wn++;
		if(s[i]=='#')bn++;
	}
	ans = wn;
	if(ans>bn)ans=bn;
	printf("%d",ans);
}